To the original poster, how bad is really bad? You need to have maths at C or above from GCSE days. That is the only official maths qualification you need to be an Officer/Pilot in the RAF. So I guess if you havent got that then you may be in trouble. Although you can resit your GCSE if you need to.
You could improve your maths with some specific self help and private tuition in the more applied areas of maths, you dont have to be able to derive Pythagoras theorem to fly a jet although you DO need to be confident with mental arithmetic in the air as you will appreciate from the PPL flying you have done.
Dont let it get in the way of your ambition though, nothing is impossible....................
DS