Don't you need to do practicals for chemistry? I thought a small part of the Chem A Level marks comes from a practical. Anyway, stay at school! You would have to be v dedicated to stay on top of all the work without having a school timetable. I know if I had the option of staying at home to study during Yr 12 I would have done precisely nothing all day. Anyway, you will have study leave at some point to study at home. I used to hate school, I found it difficult to talk to anyone and to concentrate etc but once I did my A Levels and went to Uni, everything was so much better. Focus on getting through school now, knowing you will have uni (and study leave) to look forward to.
Hope this helps! Also, great choice of A Levels, those were what I did too. Also, if you can do further maths and chem, you can definitely do Physics too.