Firstly, breatheeeeeeeeeeeee.
Advice I would give to a friend in distress (I do bio, chem, maths, and further maths, in y12) - split your revision into these three components - understanding, memorisation, and exam practise/application of knowledge. It is far more effective to memorise after you have a good understanding of a topic and why everything works instead of just memorising random facts which make little sense. When memorising, incorporate active recall - I've heard anki is really good for this. You can use ai to make your flashcards or handwrite them, but personally, I'm not a fan of flashcards and prefer blurting, but this is subjective. After memorisation, complete as many past exam questions as you can. This is my rule of thumb when revising.
In terms of working, I recommend using the pomodoro technique - 50 minutes intense study, 10 minute break. I usually listen to some music because it gets me in the mood for studying, but music isn't for everyone and might be a distraction so this is subjective.
In terms of the exercises for maths, if you are confident in a certain style of questions, then cherry pick. If not, then do as many as you can. Focus on your weak topics instead of wasting time on stuff you already know.
Resources I would use - the specifications, which tell you EVERYTHING you need to know and all the topics and skills you need. Websites, such as PMT, save my exams. Youtube videos - Miss Estruch biology, Allery Chemistry, TL maths.
Hope this helps! feel free to ask for any more advice