You're spending something pretty expensive here. And a lot of it. Something many year 12s are told is to not waste time when possible but most of them end up procrastinating and then cry in guilt because they spent 3 hours on games and other things which make them forget about what's ahead of them.
Since you need a 90+ atar for your course, you can't be like the others. Also, when you said you have short term memory and a slow mind, that deserves a Cap-Of-The-Year award. You DON'T have short term memory loss OR a slow brain. Instead, you are demotivated.
Now, what's done is done. Everything that you talked about is the past. We don't care about the past. Time moves in one direction and so should you. I, personally, feel that you should practice mindfulness for 5-10 minutes before you study just to clear your head of any regrets, distractions, insecurities and whatever you have which is negative. THEN, begin from your year 11 content and clear everything you don't know. Like, do that right NOW. Go to youtube, your textbook, your teacher or someone here on Atar Notes to get help and try clearing your doubts and gaps so you can catch up.
As for your question, if writing notes is something you think works for you, then go ahead and write compressed summaries of what you learnt. If you feel that it will make the situation worse because it doesn't help you, then do what works. Once you have learnt what you need to know, start immediately on practice tests and do tons of them. I won't sugar coat this, but you should have explored your study habits and learning style even before year 11 to get a 90+ atar. That being said, it's still possible to get 90+ but you gotta work your ass off to get there.
Good luck, and don't waste your time.