"Should I be doing more?"
Simply put, for any subjects, the answer to this question ultimately lies within yourself. Do you think doing more work will increase your understanding and your exposure of the variety of questions on a particular topic or subject? How much more work can you do? What ATAR do you want to get, what marks do you desire-and do you think the amount of work you are doing is suitable for the marks you are aiming for?
Ultimately, you should spend your time according to which subject is the hardest and which subject you are also performing the worst in. You will know whether you should be studying more by establishing short term and long term goals such as marks, ranks, etc-and if you can achieve what you desired with your current work load-it means what you are doing is enough, if not, you probably should be doing more (again, it is hard to advise as you haven't disclose what your tutoring homework usually is-how much is it and how often do you get prescribed homework). You should probably include some past HSC questions in all your subjects as practice under EXAM CONDITION(provided you have attained a complete understanding of key concepts before you attempt any HSC questions).
But regardless what you do, the most important thing is to make sure you are doing full working out and checking all your answer with the answer given or get your teacher/tutor to mark your homework, and make sure to avoid making the mistakes you have made again to maximise the purpose of you doing the work allocated. Hoped this helps a bit and my best wishes for you to have brilliant results for the HSC year