As someone who has spent 3 years teaching that stuff, its a shame to hear you saying that. You will probably remember far more tomorrow morning when you open the paper. Trust me. Most of it will come back when you start asking questions. Don't give up.
Don't worry lads, was in your position. Basically missed the first 3 years of secondary school to absence (sub 20% attendance) My attendance in year 10 and 11 was about mid 80's and tbh I messed around when I was in. Got 100% in my chemistry exam and A's in everything else. GCSE's are a pile of w*nk!
My problem is nick, I havent learnt a thing to 'remember'.
I didnt go to the best school its safe to say, my class was rough before i was put into triple science this year. My chemistry teacher only turned up to 3 lessons in two years because he was afraid of some students, which happened to be female. So we had cover teachers that made us do worksheets every lesson, gaining 0 knowledge about GCSE chemistry. So i am quite literally screwed.
Nick's right on the money. I felt terrible before my gcse science exams but was relieved after I opened the papers, so long as you have a basic idea you'll do fine. Bloody bohn haber cycle or whatever it's called f*cked me over though