As a retired Engineering Officer - well done. All the above is good advice - concentrate on IOT first - try to do it once not twice.
I'd just like to point out that you are going to be an "Engineering Officer". A JEngO is (usually) specifically the junior engineer in charge of aircraft at first line - I only did one such job out of seven tours in the RAF. There is every chance you will do other jobs like second line aircraft (if you're lucky) or OC GEF at a non-flying station (less lucky). But whatever you do it will only last for a couple of years or so before you move on, so give it your best regardless.