If you KNOW you have the ability, and you really love maths (listen to yourself, not anyone else) then you should think about doing it.
Again, assuming you have the ability, there is nothing you cannot achieve in an exam if you have the self-belief enough to want to do well at it.
Exams are all about practice and preparation - not to mention having the balls to know you`re going to "kill it"!
I found the best preparation for my exams at uni (I was never much good at exams at school, so this is just from a university point of view) was, I`ll admit, a little unorthodox:
I got into meditation - not in a big way, but I learned enough to concentrate my mind on what I wished to accomplish, and meditated on it.
Also, in my exams, I would take a packet of mints (specifically polos) with me, and after each question (during which I would breathe as relaxed as I could, I would pop a polo, and sit there with my arms folded for 1 munite to relax myself.
I never got below 84% in any exam! - from being crap at them before uni!
- brief advice, I know, but I hope it night help somewhat