Oh cool, I do same as the thread starter but also biology on top (ugh). I wish I had taken English lit, because I love literature.
The best advice I can give for physics is bombard yourself with mark schemes. I don't know if you're doing mechanics 2 but that is difficult as hell even for the smartest people in my school. If you need any help, I'd be glad to give you a hand because I'm pretty confident with my knowledge of the syllabus, and they say you retain 90% of what you teach.
Which university were you planning to go to? Oxford isn't as hard to get into as it sounds, from the research I've done on the application process... but hell what do I know?