It's doable.
Generally getting around an 83-85 raw mark in the actual HSC Physics exam will give you a nicely aligned Band 6 score.
In my opinion, the best way to improve your chances of scoring a Band 6 is to keep doing practice questions from past HSC papers and checking and improving your responses afterwards.
Remember that exam technique (time management, response structure etc.) is important for scoring a Band 6 in almost any subject.