Struggling to answer past paper questions

Hi, although I've not had this problem personally, I would recommend that you look through some past papers that either have model answers or look through them in tandem with the mark scheme for that paper. This should hopefully help you to understand how to answer the questions or to see what it's actually asking of you. If that's not really the issue, it's probably a case of actually recalling the content, in which case flashcards or mind maps might be the way to go.
If you're struggling to find resources to do this, have a look at the PhysicsAndMathsTutor website (it's got other subjects as well). You'll find past papers, mark schemes as well as flashcards and mind maps.
As a side note, don't worry too much about mocks this time of year because they don't really mean too much. I sat my GCSEs last year, and unless these results affect the classes, they only really reflect on the school and won't affect you so much. Around February time mocks are more important but they still don't actually impact your final grade. (Which is different at A-level, as an example, because those mock grades determine your predicted grades that go with your university applications.) Good luck and let me know if I can help any more. 🩷