Don't worry about it, Jade. I had braces for a couple of years and it didn't hold me back. I can't even remember which grades etc I took while wearing my braces, it made so little, if any, difference. Originally I had a removable brace (which was much bigger and more intrusive than a fitted one, which I had later), and I thought I'd always have to take it out to play my flute, but I only took it out a couple of times and then realised I didn't even need to bother. I agree with Meg_lili though, if you've only just had it fitted when you take your exam, do tell the examiner, you might as well!
Good luck