Firstly, you don't need a degree to become a pilot. If you really want to be come a pilot, don't saddle yourself with extra debt. You'll have enough from flying training.
Secondly, get a job. You'll learn a lot more about life and "grow up" a lot quicker.
I worked at a university for over 8 years. A full time student doesn't really gain the life experiences that working gives you unless they're working part time as well. Of course it's a generalisation but after seeing thousands of students both full time and part time I think I can speak with a fair degree of experience. Consistantly, the mature age/part time students got the better grades than the ones straight out of school. (Science degree)
If you cut a class, well, you can catch that up. If you don't turn up for work without ringing etc, you'll face a pissed off boss.
If you want a degree, why not do it part time whilst working? This way you'll finish it at ~24 or so and you'll have 4-6 years worth of employment. If you plan that well, you'll have industry experience in what you've been studying. So, if heaven forbid, you lose your medical or your flying job, you can go back to your previous job.
So, my advice is: Get the best possible grades at school. ie A levels etc.
If you really want a degree, pick a subject you like and study that. (Only problem is, if you want to become a pilot, then aviation is what you're interested in..Aviation degrees are well... useful-ish in aviation)
However, get a job. You'll need the money.
*I don't have a degree - I had all the fun of being at uni and I got paid to be there.*
I do have a cool job though.
