my Maths GCSE I achieved a grade C (9 marks of a Grade B), by no means excellent - but its a pass
Sorry to piss on your parade, but that's your problem - a grade C in Maths isn't enough for an aircrew (P/WSO/WSOp/ATC etc) pass. It's a pass in the eyes of the AFCO, but the ability it demonstrates is way short of the ability required to pass at OASC.
You might be able to turn it round, but it'll take a lot of effort.