Save your money, and do not go to a maths brush up course. I did, and it was a waste of £200. They said 10 hrs, I got 5, since they assumed you did not know how to add, or what a number was.
I have a maths O-level, and gave up Physics when I was 14. I got through the ATPLs OK.
Buy some good GCSE books. There are quite a few available, so have a look through their different styles and select the one which will suit your learning style.
Good ATPL notes will walk you through the theory and background you will need in anycase.