I have my IGCSE science exams in a week for Chemistry Biology and Physics and i have only revised about a 1/4 of each subject and i really need to get an A* or A otherwise i can't do a-levels someone please tell me the best way to revise in short time or how to get at least 80-90% in the exams.

i have been really scared as my whole future depends on these grades after failing them last year i am in college doing a computing course while taking the exams in a private college and because of the college work i haven't had enough time to revise.