I think ive practiced my exam pieces too much...im beginning to hate them. Will this affect how well i perform in the exam?

I feel like that sometimes. Here's what I do - if it gets to the point where you really can't stand to play the pieces anymore, just leave them for a week or so, and muck around with something toally new. Then I go back to the exam pieces, and I feel 'refreshed' (if you know what I mean).
NEWay, in answer to the question, it didn't do me any harm practicing too much, I just needed to take a break occasionally.

I remember that feeling well - it's a problem I think teachers should bear in mind when preparing candidates for exams.

If I was sitting exams now I'd try and make sure I practice at least one piece not related to the exam for every exam piece. If these other pieces focus on a similar range of techniques to your exam pieces then all the better. For example, if one of your exam pieces requires some high playing, or is particularly chromatic, then complimentary pieces should be chosen to continue to improve these aspects of your playing, while ensuring you don't get bored stupid! This should actually make you a better player too - no danger of just learning pieces 'parrot-fashion'.