Sorry about your exam, that's too bad.
Like someone already said, start off by recording yourself and posting it here, there are plenty of people the can help you out.
Something else you can consider (Though unusual) is revising your entire way of playing the piece for a while. Sometimes when you play a certain piece for a long time (Like you said you did,) it gets a bit "stale" (And it's difficult for you to notice, but other people do), maybe that's the reason you didn't pass.
A good way to freshen it up a bit is to pick up a whole new interpretation. Try listening to different preformances on youtube, pick the version you relate to the least, and try copying it.
Play only that version for a while, and only once you think you've mastered it, start over from scratch, and make up a brand new interpretation, that you think is best.
I know it sounds a bit strange, but it works. But try saving it as a last resort.
Best of luck, if you do the exam again tell us If you passed!