I revised a level maths in year 10 summer. I just did C1-4 briefly. I am taking additional maths which is some C1-2 topics and some M1 , S1 , D1 together. It is made for year 11s which have studied some alevel maths. It is a level 3 certificate. I suggest you try to understand rather than memorise, for example SUVAT proof and stuff like that. Do past past papers , watch videos ( they really help). If you still find this difficult and don't think you can get an A* , I suggest you just do Alevel maths in year 12. Try out additional maths , you can only sit it in year 11 so you might aswell get an extra qualification and it's a lot easier. Finally make sure you can 100% get an A* and that getting there doesn't distract you from GCSE as they are more important right now. Learning C4 will be even more harder. You should just learn content as soon as you can and do past papers.