if there's time before your exam, have your flute checked over by a good repair-person, and just generally cleaned up etc - there probaly isn't be time, but if there is... especially if it hasn't had a service in a while.
if not, ask your teacher to have a look over it just to check whether any of your pads are leaking or anything and get them to have a play on it and see if they notice anything that seems wrong - probably the most important thing to do.
ask your teacher if they have noticed/whether you are doing anything wrong.
after the above, then find yourself some good tone exercises and work on them carefully and thoroughly, and try to really support the sound especially in the top octave.
unless there is something that has actually gone amiss with your flute, which hopefully your teacher would be able to work out, it may well be that as you have progressed, and especially now you are working for an exam, you are concentrating hard and listening better, and your ear has got more sensitive, so you are noticing things that you didn't notice before and are becoming more picky with how you want yourself to sound... which probably means it doesn't sound half as bad as you think. if that makes sense. the other thing that can sound icky/fuzzy in scales is when you have a note change that requires more than one finger to move at a time, eg B natural to C#, if those fingers are not moving exactly in unison. slurred scales are good at picking out weak points that way
first things first, get your teacher to check out your flute in case there is something wrong, but if they think it's fine and unless your teacher suddenly also thinks your scales sound fuzzy, it's probably just you hearing yourself with more sensitivity and accuracy... so don't worry in that case because it's a good thing!!!