Don't worry too much about extra methods classes, it's much too stressful. If you do a bit of extra work in the holidays and then make sure you understand what's going on in class and do lots of practise questions you'll be fine. It's important not to fixate on your weaknesses, and trust that with time and practise (and help from us/your teacher) all your methods issues will sort themselves out. I started methods this year being seriously worried about the course and having to compete against the whole state in a subject that I perceive to be one of my weakest, but I shouldn't have wasted my time worrying because it all came together eventually - without extra help. And I'm sure you're better at maths than I am

Also, to some extent I think it's true that there is a limit to how much you can achieve in a year. For example, if you got all E's for your years at school, you probably won't get to A standard by the end of year 12. Obviously, your maths skills will develop throughout the year, but your skills will develop for all your subjects. You can't expect to improve in methods to such a large extent that a C student starts getting As, unless they're doing other maths subjects as well or they have neglected their other ones, or they've gone from really wasting time to being totally consciencious. I mean, I'm a big believer in working hard and doing your best, but realistically, you can't expect to improve that dramatically within a year and putting that much pressure on yourself may be unhealthy.
I don't know if these thoughts are relevant to you or not, but that's basically what I think about programs which say that they'll transform average/below average students in to brilliant students.