Am I doing enough?

I'm a few weeks into my first year of A Levels, and I am really enjoying it. All the subjects I've chosen are subjects I really enjoy so there's no problem with doing the work; I'm just worried I'm not doing enough. Everyone has basically scared me into thinking this, because I'm constantly being reminded that "there's a huge jump from GCSE to A-Levels" but I don't feel like it's hit me yet. I'm doing fine with coping with the homework work load, but I'm not sure I'm doing enough of the extra reading, note-taking and revision prep; I feel like I could be doing more. The last month has been pretty hectic as I work Saturdays and have been doing NCS on Sundays, so I've not had as much time as I usually would (now that NCS is over, my Sundays are free), but realistically how much more should I be doing outside of class?

If it helps at all, I do Maths, Chem, Physics and History.