My AS grades were ABBBU.
with 2 exam resits alongside my A2's I ended up with A*A*AB at A2, and I'm fast tracking another A2 in my gap year predicted at A*
DO NOT GET HUNG UP ON YOUR AS LEVELS, honestly with a bit of tough work they're easy to turn around
However,
unless you're at the top grade boundary of the B, I would probably recommend resitting your AS exams with the B's in (ironically my A*'s came form the subjects I previously had B's in, not the one I got an A in). it seems like a lot of extra work, but your A2's complement your AS's, so a lot of the time it's almost like revision. Also you're working on your exam skills whilst doing your A2's and that's probably the most helpful thing
Resitting these AS's also takes a little bit of pressure off your A2's so it's not all just sitting on one exam to get a ridiculously high A