A variety of thoughts in this thread.
No-one can give you a magic crystal ball story tailored to your specific needs and wants - whichever way you go is for you to choose (take a gamble on, really).
However, one of the big problems is that, at your age, you don't have anything like appropriate personal experience to make a rational, considered decision so, whatever you choose remains a bit of a shot in the dark (though you, like all of us at that sort of age, considered we knew far more than we did). Particularly if no-one in your family has a tertiary or trade background, you have little chance of obtaining sound advice.
I can speak only of uni stuff as that was my path. However, don't underrate a sound trade. Many of my classmates went that route and did just fine for themselves. One close mate did that (E&I LAME) and then went on to elec engineering and a masters and has done extremely well for himself. Others screwed up badly, made a welter of things at uni, and, having nothing better to do with their time, ended up with PhDs in tech disciplines.
One of the advantages of having a couple of strings to the bow is that it gives you more options than with the "all eggs in one basket" approach. Particularly with flying as your goal, the medical is a real potential risk all through your career albeit that, at your age, one is invincible and gives little thought to any downsides to one's future - just like we all did back whenever.
One very important consideration is that you really don't want to end up in a job/career which you end up hating and then find marriage, kids, mortgages - all those time and dollar hungry things - conspire to make it very hard to opt out and start again. So try and make your first punt a good kick, as it were. Knowing a lot more now than I knew back then, I am glad that I didn't go my intended path (medicine) - I would have been driven to distraction in a few years of practice !
Another story - mine - for what little it's worth.
I completed my PPL in my final year of secondary education (I was very fortunate in that I picked up a RAAF ATC flying scholarship).
Headed off to uni to enrol in medicine. Had a coffee at the Union and, while flicking through the Handbook, came across engineering. At that stage, I had never heard of engineering - I though engineers were the guys who fixed cars at the local garage (did I mention about the problems associated with not having anyone in the extended family with a tertiary/trade background ?) Came across aero engineering - I've got a pilot's licence, thought I - bugger medicine and promptly enrolled in engineering - I still shake my head at the all of 10 minutes (more like 5 minutes) consideration I gave to a career at that point.
Started engineering and CPL in parallel (again, very lucky in that I picked up a DCA flying scholarship for the CPL). Took a year off after first year to concentrate on the CPL (had a couple of interesting jobs to support the dollar needs) and then completed the CPL in second year. Considered a double degree (eng/sci) but decided not to spend the extra year at uni (although I very nearly had enough subject credits for both by the end of fourth year).
Completed my ATPL/SCPL subjects in parallel - and, then as now, the subject difficulty was not a major problem but the time and pass mark constraints made, and continue to make, the subjects rather difficult to pass - certainly more difficult than uni exams.
Started out with an aircraft OEM in the design office and later went to a smaller airline as a tech services engineer. A bit later on, very lucky to get into Ansett (thanks, Henry) with not very many hours compared to those in my intake cohort. I have no doubt that my engineering background was material in that and that I was looked at for later useful potential. Subsequently picked up ANR (and, later, CAR) design delegations and continued to run a reasonably successful aviation design consultancy in parallel with the flying activities.
Now sort of part retired and involved with pilot theory training and operations engineering work.
Would I have changed things were I to have my time over ?
Well, in respect of this and that, I guess so, but, overall, I've had a ball and kept the wolf from the door. So I've been fortunate. I'd probably be silly enough to bin medicine, again, and sign up for aero eng, as I did back in the 60s.
Now that I've waffled on far to excess, what might be the take aways ?
First, don't skimp - there are no shortcuts unless you have a very rich, very generous daddy or you pick the right numbers in the lottery. Try and give yourself some options, considering that you will be, to a large extent, having a stab in the dark when it comes to what your likes and dislikes might be in 20 years' time.
I can only talk of my own thoughts - I have been involved in Aviation degree training - nothing wrong with those degrees overall, but they are not really marketable outside the Industry and, even then, of limited value beyond the fact that they attest to an ability to do some study and pass some exams. Whatever path you might choose needs to be marketable for some decades down the track. Be aware that, unless you can do some relevant work in parallel to the flying, the other skillset will become stale and not necessarily as useful after 10-20 years totally away from that game (unless your major was basket weaving with a minor in drinking and carousing - they will always hold their value).
If your hankering is tertiary level stuff, I would go after marketable degrees (within the constraints of your discipline preferences - there is nothing worse to me than the thought of ending up in a detested career). Degrees such as engineering, law, medicine, commerce, science (probably with some post grad work), accounting and similar, would be a starting point.
Some folks have taken this to extremes. I well recall dear old Ralph Capponi (who some of the older folk will recall with a smile on their faces). Ralph flew as an F/O with ANA (-6s, I think he said - he was a contemporary of Pontius), somehow managed to do his MB,BS along the way, qualified and practised as a GP, subsequently did electrical engineering, and ran a quite successful avionics business at Essendon for many years. A most interesting chap. Gave up the airline flying but continued to play with some nice GA toys used as avionics demonstrators. Can't recall the rego, but I flew his 685 once or twice and that was great fun.
Tertiary level stuff, though, is not the be all and end all. Nothing wrong with a good marketable trade. Trades such as plumbing, electrical, building, mechanical and similar might be worth looking at.
Main thing is to try and not put all your eggs in one basket. Especially with flying, it is one of the few careers where you are at the mercy of medical misfortune and a career can be extinguished overnight if you are unlucky enough.
So what to do right now ? Knuckle down and get the best results you can in your matriculation exams and then the world can be your oyster.