Although we were always told that GCSEs were all important at my school (private, london, day) I totally messed them up -
2 A*, 2 A, 3 B, 2 C (in dual award science - bastards!!)
I still received an offer from St. Peters (Oxford) to read French Literature.
My school was really negative about me applying because they thought id just get slapped in the face about my GCSE results, but in the end i was 1 of the 5 (out of 40 who applied from my school) who got an offer.
What im saying is, once you've taken your GCSEs there's nothing you can do about them, so theres no point worrying about what the Unis will think. Just make sure you have a really good personal statement (show loads of enthusiasm) and make sure your teachers / reference writers believe in your capability in the subject.
In the end, my French Lit tutor cared about whether or not i was good at his subject, not about whether or not I had memorised the periodic table.
Good Luck! I'm sure you'll be fine!