Hi, I am in year 11 so haven't done my GCSE's yet but I would say to relax a bit in year 10 (until your mocks, revise for them). I didn't really do much revision in year 10 but now in year 11 I am focusing and my grades are mainly 8's and 9's (an improvement from mainly 7's and 6's in year 10).
However, I would say if you have teachers who can't teach or your school doesn't have teachers who are qualified in what they are teaching like mine just do the content yourself. I wish I did this for subjects like physics as my teacher says he's never passed GCSE physics exams before.
Also, English literature is catching up to me now just try and make your revision resources for paper 1 in year 10 (not necessarily now but sometime in year 10) as my school teaches paper 2 in year 11 and I am only just starting to make my Macbeth revision. Re-read your texts over the summer as well it will help.
Most importantly when you revise use the specification. I cannot stress this enough especially for science, them CGP revision guides have a bunch of unnecessary information you won't be asked about on your exams since it's not on the specification. For science, free science lessons on youtube has videos that follow and stick to the spec exactly so he's better than cognito or CGP.
For maths just do past papers, past questions, 5 a day corbett maths questions. It really is the only way you can revise for maths. If you are consistently getting a topic wrong watch a video on it and then just spam past topic questions (I think you can find on PMT). I think the blokes called GCSE maths tutor on youtube, I'm not sure but there's a grade 9 playlist you can watch and it has the hardest skills on the paper so watch that.
Just so you know year 10 is the time for making mistakes, revising in ways that don't work and then correcting them heading into year 11. You are not going to get it right first try but making mistakes in your revision now or in your year 10 mocks means you are focused when in year 11. I would recommend just try catch up with notes, flashcards etc on topics your studying now (mainly paper 1) so in year 11 you can focus on paper 2.
Please keep on doing all of your extracurriculars, dropping them in year 10 to revise is not going to help anything as these are outlets for stress (I wouldn't drop them in year 11 either). Your revision should not be so extensive that you have to quit seeing your friends and doing extracurriculars as you are still a teenager who should be doing teenage things.
Don't compare your revision to your friends as always quality over quantity, I wouldn't spend over 30-45 mins on weekdays and 1-2 hours on weekends revising in year 10 (even this is way more than I did at this point in year 10), your friend seems to be taking it too seriously.
This was a long message but if you have anymore questions, happy to help.