I would think deeply about whether self teaching is something that you have the strength to do. There will be topics that you will not understand, especially in C3 and C4. This means that you will have to do as much research until you do, rather than being able to rely on a teacher to teach you. You could hire a tutor for maths that could help you with these topics and get you up to scratch. For A Level Maths you have 4 core modules, and you take two in the first year (C1 and C2) and you also have 2 other modules of your choice and you take one each year. These can be mechanics, statistics or decision. I would suggest taking out a core 1 book from your library and seeing if you think the content is bearable. The best method of revision for maths is by far past papers, you will struggle to run out. Good luck. TSR is also here to help with maths if you need it!