Can you get an A* in A level business without the help of a teacher?

Im resitting 2 of my a levels this year and I've picked up a level business to complete in one year. Problem is, I have to study it independently without any help of a teacher. This includes marking my papers. I'm stressing a bit because the edexcel a level business spec is so vague so I always feel like there is a little a bit of content I'm missing from the youtube videos I'm watching and the cgp book I'm revising from. I'm also stressing because I've heard that the marking is quite harsh and if I'm marking my own practice papers it won't be as accurate as the marking from actual examiners. Are there any revision resources that definitely cover every point I need to know? Also, am i right to be stressing about this stuff? (For context, I do maths and physics as my other 2 subjects so I haven't really done any essay writing in a long time)