ohhhh 2 months! I think if you do a past paper right up until you have exams. you don't necessarily have to be done with them because you are using it for revision. however I would leave the most recent paper like 1 or 2 or even 3 FULL past papers to do a day before the exam. for biology, leave the recent may/june 2020 as well jan 2020 and oct 2020 if you have access to them until the end. and whatever mistakes that you get, go through that topic or sub-topics again. that's what i did and you should've definitely started studying already even if its just a little bit, this way you have less pressure at the end, less things to cover as you know them already.
Hopefully this makes sense!