The Cambridge Checkpoints Science consists of 4 parts:
Take a look at the Framework, print it out and check whether you know it all.
In my opinion, Scientific Enquiry should go well, you practiced enough during the science lessons. Do the questions of the exams and see whether I'm right.
Take a look at Biology. We covered almost everything the last two and a half years, but this doesn't mean you still know it all. Your 3th form Biology textbook contains almost all subjects, so look up the topics you don't know anymore and study for the exams.
Practice all the exams to the right. They show you what to expect.
Go back to the 3th form