Firstly, I'd just like to say well done for not being stressed haha. I wasn't either when I did mine so it's definitely normal. If anything it helps you recall information better so that's good
Just as other posters have said, revision is different for everyone. Teachers at my school kept trying to make us draw up revision posters and make really good notes, but I found that personally, I learnt best by reading through my notes without any distractions (ie. no music/YouTube or anything that might possibly distract you). That said, making good notes is really important and use as many colours as you can (my notes look like rainbows)
For physics, I found that once you know the material and do a few past papers, it's a waste of time to slave over any more. Instead, I'd recommend looking through them and highlight any questions you aren't sure about, then just flip to the markscheme and learn the answers. (Physics is weird like that) For Chem/bio, I'd say just make sure you understand the concepts rather than purely memorising facts.
History I'd recommend you to selectively revise, since it's pretty impossible to learn everything on the syllabus. Our teacher gave us the predicted key questions and got it right
, so definitely see if your school keeps track of past exam trends.
My school did a mixture of Christianity and Buddhism for RS, and I'd say don't even bother learning anything from the textbook for Christianity. Memorise a few quotes for each topic (the broader the better, since you can reuse them across questions), and also the key terms.Maths and Additional maths was just a matter of cramming for me, but I generally have a decent grasp of it so it wasn't too difficult.
For I GCSE maths, if there's a small topic you can't understand, just skip it, since it isn't really worth it. Focus your time on sections you can perfect instead.
English Language and Literature I didn't actually do any revision for, except learning key literary terms. Since there are passage questions for lit, it's more important to know the book generally.
Spanish and Music were again really just last-minute cramming, but for languages generally, I'd say learn a few general idioms that you can use in the writing paper to wow the examiner.
Best of luck and just remember to stay calm