BTEC L3 applied science and a math resit or Alevels?

I've only had 1 year of GCSE education at england due to the fact that prior to this i had to move abroad. This has affected my chance at choosing what I want for ALevels since my school has alot of restrictions for sixth form sciences, I've not really had the best education since I've moved through 3 different schools, I took a few entry exams at the beginning of last year when I applied to my current school and I ended up in foundation for all my subjects, which was a nightmare because I knew that C was the highest you could get. I knew that if I put in the effort I could move up so I caught up w the english cw from year 10 and taught myself year 10 content in science. Thankfully, I managed to move up to higher for both english and sciences securing A*'s for my coursework.At this point I was getting C's for math since I was doing foundation and knew I had to move up to get atleast a B if i wanted to do Bio,chem etc for alevels but my teachers said its too late in the year to move me up so overall my GCSE grades were;
Religious studies - A
Art - A
Urdu - A
Core science - B
Additional science - B
English - B
Maths - C
I have no clue what to do I've applied for a BTEC Extended diploma level 3 in applied science at college since its the only one w easy entry requirements but is there other Alevels that I could possibly do with these grades? should I take a resit for maths whilst doing this btec and then after im done w both do bio chem math alevels? I'd really like to pursue a career in anything science related PLEASE HELP!!