I got an A in OCR bio so hopefully, my advice with be of some use. Basically, what I did was learn all the content without the help of school by January by making notes on everything in the CGP books. However, if you do this your mock grades might drops, as did mine, as your most focused on covering the content. After that, I went through all my notes and made flash cards in ANKI, and reviewed these until the exams started. In the end, I think I had thousands of cards just for bio. After the cards were made, I did as many past papers as possible and went over the questions I didn't get the answers with my teacher.
Do you think you could share your biology anki decks?