The only way you can get a C is to revise, revise & revise! From now until the exam, do some maths questions every day. Go online, do some past papers, work sheets and if you get stuck, search for YouTube Videos. This will help you to understand and practice the routine when tackling questions in the exam. YouTube videos really help as you're being visually guided through types of questions and it's similar to having a teacher there. Keep at it! Good Luck!