You'll be fine

At the beginning of this year, I was also like "omg legal exam is ALL of units 3 and 4" and it is a lot, But the best tip I can give is to study for your sacs as though you were being "VCAA EXAMINED" for that area of study - this isn't just to ace your sacs for good ranking, but also because it doubles up as exam study. Don't JUST study the revision sheet your teacher gives you before a SAC...Know every dot point for that area of study inside out. It might seem annoying studying so much more than necessary for that sac but it WILL help in the long term. At the end of this year, I found it so much easier to study for Legal exam (rather than cram) because the information had been established well the first time (when I was studying for sacs) and through constant reading and explaining it to myself up to and during exam period it just STUCK.
Also in psych, you'll learn about something called "relearning" where the information you learn is never really gone as such, there are always traces of it. The more you go over your notes, the better and more long term that information will stay in your head
and also use mnemonics - they are SO SO helpful