OP, when you say these scores were not necessarily 'true reflections', do you mean that the assessments themselves were easier than an ordinary, run-of-the-mill HSC exam? Because if this is the case, you might be got a tad off-guard with the half-yearlies because trust me, it's a totally difference experience.
Accordingly, the best way to prepare as Kolmias said is to just smash those past papers, particularly for the subjects you're unsure of. It's a bit early but I'd also try submitting some practice essays to teachers for feedback, maybe even a redo of an earlier assessment task if you haven't done so already; I know this worked well for me during my half-yearlies. If you're glued to your device, a tactic that really worked for me was setting a 50 minute timer (acting as a study block) with 10 minutes set aside at the end for a break. Rinse and repeat.
You should try and tailor your study pattern to your sleeping routine too, adjusting it according to the unique requirements of your body. In my case I only needed a good 4 or 5 hours of sleep a night and I was good to go; I used this to my advantage. If you're ok with less sleep or can wake up later, a 7 PM start is ok, provided the study you do is effective, targeted and sticks with you.