i'm in exactly the same boat, i got 2 A*s, 3 As, 3 Bs, 1 C and 1 D in the mocks with absolutely zero revision - even the night b4 + i was really ill the whole week so i made some REALLY daft mistakes.
but even at this point, having done 1 gcse exam, the only subjects i've even revised a little bit for are english, maths and science. i'm seriously wondering whether i'll be able to cover the two history modules, 6 for graphics, the whole course for business (we've had basically no teaching for this one) and spanish over the next few weeks.
i'd say its better to start now and get SOMETHING done, than give up completely b4 exams even start - u never know, last minute cramming at GCSE seems to work for a fair few, maybe we'll be lucky? lol