Whether you get Band 6 or not in Maths basically depends on how much time you work for them.
I sincerely think that Maths exams' results truly reflect how hard you worked (like many subjects).
If you really want to excel in Maths, you will have to put at least 1 hour a day for it. For example, I put 2 hours a day for them even on weekends just to understand, revise and finish questions. And sometimes they really pay off.
It seems a very simple advice, but it is the best advice anyone can give in regards to Maths studies & problems.
For more information just PM me and I will help you with more detailed advice and resources.