too much information mathsWatch
If you're counting things like "how to expand brackets" as a topic, then the majority of those 300 topics will very quickly become routine methods that you will not need to put in any conscious effort to remember
If you want to raise your level by 2 or 3 grades, I'd print off the syllabus (there are about 100 topics), mark on which you've covered and which you think you have problems with.
Then, for each topic, work through something like the questions in drfrostmaths.com (or whatever package your school uses). They can be set by topic and level. Look at the videos / slides if you find an area difficult. Doing a topic a day for 15-30 minutes would take 3 months to cover all the areas, so keep at it and maybe select topics intelligently to hit the problem areas first.