Hello. I'm a year 13 student, and recently, I got my predicted grades, which are BBC (edexcel maths, aqa chem, and aqa bio respectively. I'm going to try and convince my teacher to predict me a B at least because my school is strict with increasing predicted grades

I just want advice on how to do better. I revised a ton for my end of year 12 exams but got a C and Ds, which totally sucked. I'm not really looking for pity or to be made fun of, though. I just want advice on how I can improve. Currently, I do biology flashcards whenever I remember, mostly on the bus, and I do exam questions on pmt for chemistry and also bio. And for maths, I don't even know how to revise properly except for doing the textbook questions, which my teacher recommended when I asked for advice. I mostly just feel like I work so hard before my exams, but I never seem to get the best grades. Like I feel like I go into the exam feeling like I know the content and then I don't get anything like the questions confuse me, even though I do past paper questions at home.
I want to achieve As in my real exams and I have mocks in a couple weeks so hopefully at least improve my grades to all Bs by that time, which I know will be difficult but I'm willing to try. If anybody has advice on how I can achieve this, I will be forever grateful.