It's really hard to predict study scores. The reason it's hard to predict is because your SAC marks don't matter. What matters is your rank and your cohort's performance on the exam.
Your school's SAC scores will be moderated based on how well the students at your school do on the end of year exam. If most of your school gets between 70-90% on your SACs but then gets 40-70% on the exam, it means that your SAC's are easier than VCAA standards - and the same is true in reverse, if everyone does better on the exam than they have on the SAC your SAC marks will be moderated up.
If you're comparing your SAC scores to people from other schools, don't. There is no point, as I said above you can't compare SAC percentages between schools.
I know you said someone at your school got 96%, but is that just one person? Do you know for sure that they got that? Often when we're stressed everything gets a bit overwhelming and it seems worse than it actually is.
I mentioned earlier that ranks are what matters, if you know what rank you are (your teacher will know but may not tell you) then you can look up how many people got 40+ at your school each of the last few years and use that to figure out what your chances of getting a 40 are.
Ranks are separate for Unit 3 & 4, so even if you had a low rank for unit 3 you can still get a good rank for unit 4.
Good luck, if you have any questions about the content or studying, feel free to post them and we'll do our best to help