Don't worry Dazed, everyone will be feeling nervous and anxious about the HSC exams, as well as awaiting for HSC exam results/UAI.
I am in the same situation, as with everyone else. If you have a 'top' assessment mark, and perform extremely 'bad' in the HSC, say 60, 70 which is below your usual standard, it will, of course, affect your final HSC mark.
In my situation, and I would imagine in yours as well, we/you would have to get 90% PLUS, in the HSC exam to maintain a Band 5, if not a Band 6 HSC mark.
Ideally, 94 to 96 would guarantee the 90+ HSC mark, but we'll have to wait and see, given your current assessment mark (parallels with mine), and the difficulty of the HSC exam itself