It does pay off
I finished last year, on a gap year atm
I had BBB. But I did OCR B Chem. Have you got a CGP revision guide for biology? It was a total saviour for me, and I know I would not have done so well if not for that; it has a little bit of added detail in places, but I found that made it all make a little more sense.
Maths, just do as many past paper questions as you can, the exams seem to be designed to confuse you. But don't panic about it, practice makes perfect when it comes to that
For chem, there's a salters OCR revision guide that is really good, in that it puts everything in a logical order... I think theres one for OCR A as weall as B, but this combined with another CGP revision guide was great
Also, I failed every mock I ever did. So if this happened to you, don't panic
Hope this is a little reassuring!