Hello!! I can't imagine what you must be going through! As a grade 9 student, I hope my advice helps you! :]
I used a really amazing book called GCSE maths in a week by Letts. It covers all topics in a concise way and goes through examples too. You don't have to use it, of course, it's just a recommendation. If you don't want to use books, you can use great videos on youtube too. This also depends on your exam board, but honestly it's mostly all the same.
I'd say do some past papers, figure out your weak topics, prioritise those to relearn/practice and then go back to papers. Try put on exam noises, set a strict timer and mark your papers. Keep a record so you don't repeat any papers. If you don't understand anything, go back to books and relearn, or you can use videos by corbettmaths. You can also find targeted practice questions for weak areas on a few good websites, like corbettmaths again and also Maths Genie.
Try not to stress too much, don't let it get to your head, you still have time, even if it's not a lot, it's good you recognised it now. Stay calm and keep going, I believe in you!
I wish you all the best and I hope everything goes well for you!! ♡♡