Your 14!
Thinking of failing already is going to doom you for sure.
Look at local colleges.
City and Guilds offer a foundation course in Aircraft Engineering, you need nothing to get on that. Its like 4 GCSE's
There are also advanced and foundation certificates and diplomas in Aircraft Engineering and Aerospace, they are just like A-Levels the advanced ones, and foundation ones like 4 GCSE's.
Once you have A-Level type education in an Aerospace field you'll be far better to make you mind up if you want to fix the things or design them.
Engineering in aviation is vast, research it all and find what suites you.
Engineering in Aviation is also one of the top payers in engineering, with Chemical and Electronic coming a little above.
Take the advice of all above too, vast experience and knowledge.