Hi Alex.
There are some things in life for which there are no shortcuts and the only way you will achieve it is to simply suffer through the required slog.
If you *really* want a career in the RAF then you will go and get your Maths GCSE. Now that you've got your degree, and if it was as involved with Maths as you are implying, you shouldn't have any issues with taking the GCSE exams. Having said that, now that you're older and have some excellent motivation to study and work at the Maths it should also be a bit easier to get that pass.