I'm not a Revs kid, but don't worry about a subpar score on your practice exam - you have SO much time to improve!
I completed Legal last year in Y11, and our final SAC was the second week of T4, with the completion of such prompting the beginning of my exam revision. I attend a very low-ranking rural government school, so I didn't really know what I was doing with regard to studying (my teacher had, however, taught a student who'd achieved a 50 a few years earlier). My score on the first proper practice exam that I did - not even under time constraints, from what I can recall - was 82%, and this was only a couple of weeks before Nov. 14th. I ended up with a 46 after getting very flustered in the exam, but that's a different story.
I'm only in Y12 myself, but I would recommend ensuring that your content knowledge is sound (you should be working very closely alongside the study design) and that you're able to apply this knowledge to past VCAA questions. Completing practice questions is of so much more value than doing entire practice exams, but writing under time constraints is also very important.
I hope that my advice wasn't too trite, and that it's somewhat of assistance - good luck!