Don't panic - its natural to be a bit worried and you have probably not done as badly as you think.
So dont let this get you down, especially if you have other exams - keep your head up, and be confident, and 'I can do this'.
For every course at every Uni, there are usually some spaces for 'near miss' - no Uni wants to put a course in Clearing unless they have to. So you may still be accepted if you slip a grade, but of course there are no guarantees so you still need to power on with the revision and focus on any other exams to come.
Good luck!