I got a C *shrug* I'm now on a year study abroad *cough*travelling about on student finance, and am on my way to a 2:1, life is good.
Do your best, but there are many factors that go into your grade, not just your intelligence, circumstances can really mess with your grades. If you put the effort in and you still get a C, it's really not so bad unless you're determined to get somewhere that requires A's.