Yes, it is definitely possible to achieve an ATAR of 90 even if your performance in your first-term assessment tasks is not favourable. This is because there are multiple school-based assessment tasks and exams that you will be required to complete before your final rank is determined in each of your subjects. This means that there remains a significant weighting left to be determined in terms of your internal performance in each of your subjects. Not only that, but the HSC exam of each of your subjects is worth 50% of your final HSC marks alone, and therefore constitutes a significant chance for you to further improve your performance as you near the end of your year 12 journey.
Cases such as this are fairly common and numerous students were able to make comebacks. They were therefore able to successfully attain their desired standard of performance, ultimately enabling them to achieve their ATAR goal. Doing so will require determination and diligence in your studies and preparations, in addition to ensuring that you address any areas of improvement that you may have identified from your tasks.
Of course, this is not to suggest that unfavourable performance will not have a negative impact. It is possible that, depending on the weighting of each task, the goal of maximising your rank relative to your cohort may become slightly more difficult to achieve. However, it is certain that the above still applies.
I hope this helps!