You ask if 80-90% will be enough to get you an ATAR over 90 but that is impossible to tell. You cannot, I repeat, cannot, go from raw school percentage to ATAR without more information. The process would be more like the following:
1. Raw school percentage
2. Raw HSC exam mark - you haven't sat the HSC yet
3. Moderated assessment mark - this depends on how well others in your cohort went, and the HSC exam marks
4. Raw HSC mark - depends on the raw HSC exam mark and moderated assessment mark
5. Scaled HSC mark - depends on how others in the state went
6. Aggregate - depends on the combination of your best 10 units of scaled HSC marks
7. ATAR - depends on the aggregate and is a rank compared to your Year 7 cohort
You only have information for step 1.
Needless to say, your school marks are relative to your school assessments. What is more important is your moderated assessment mark, which is a mark relative to the state. That is dependent on how well you and your cohort performs in the HSC exams. Yes, you should still attempt to gain as many marks as possible in school and be as close as possible to the highest mark in school. This determines how well you will be moderated relative to your peers. But I repeat, most importantly, you and your school must do well in the HSC exams.