I got a B in maths retook it twice and got a B, now yes i hardly revised, but i still took it at A level, and put about 300% more work in then GCSE (which is turning up to lessons, not talking or misbehaving and doing every piece of HW on time) and ive got AAABA in all of my end of module tests from chapter 1-6 (excluding 4) i got rejected by alot of schools because of my B, but because of my hard work and dedication im now helping other students on their HW and stuff who got As and A*s.
So yea, if maths will aid your application, which it will, im doing Biology and Chemistry as well then take it, work hard at it and understand it.