School grades (e.g. A's, B's.. or %'s) do not really matter as much as your ranks do (since each school sets and marks their exams differently).
Also it is a bit early to really estimate where you'll land in terms of your ATAR at this point in time, because you've only done the first lot of assessment tasks. Ranks can and likely will change significantly as you progress through the HSC next year, so perhaps wait until your first report (after halfyearlies) comes out?
Your school and where it ranks is also an important factor since your cohort will also influence your HSC results.
Generally speaking though, 80+ is quite manageable and achievable, provided you put consistent effort and work.