Hi! It is never too late to start aiming higher and working harder. You can definitely get the ATAR you want. However, it will not come without hard work and a genuine motivation to do well. I achieved an ATAR of 95+ last year. Here are some tips I used to achieve my ATAR:
1. Goals - why do...
Do past exam papers! In my experience, past papers are the most useful resource for Chemistry. Personally, my chemistry grade went up by about 10% after I really started focussing on doing past papers!
Having good notes will also help you heaps! So make sure that you're staying on top of them...