I can't say anything about maths as I did not take maths, but I took both chem and bio.
I would say you should resit all the modules you did not get A's in. Thats what i did. I got AABBC at AS, resat everything apart from the A in bio (it was 94%ums). I ended up doing 7 resits, along side my A2 exams and I managed to cope. In all honesty it isn't as hard to do as they say, take lots of resits whist doing A2 exams at the same time. I didnt even start revising for the resits until a few weeks or even a week before the exam. As I know they didn't really count as much, I was relaxed and clear minded and aced all of them getting above 90% ums in all of them.
As for your A2 exams, they are the priority. Bio and Chem, lots of past papers. The same questions styles come up each year, just different examples used in them. Work harder than you did for AS for A2. Let your AS levels of effort be your baseline and just do it!
With this method of resisting basically everything, and working as hard as I possibly could for A2's I turned my AABBC into A*A*A. You can do the same too!!!!!!! Don't let AS grades get you down.