Disclaimer: I am currently studying biology. I am NOT a past student. However, I am doing quite well in my SACs and I have basically taught myself the entire course, so I think I am in an okay position to help. But please take everything I say with a grain of salt.
Given you are short on time, I would find a condensed and digestable source of information for Unit 3. I recommend Phoenix FIre's Unit 3 notes. They have the added bonus of links to short videos to help you consolidate content. In your position, I would then spend a week or two using these to try to understand the content. Mindmaps, highlighters and diagrams are your best friend here. Identify your areas of weakness and book a time to see your teacher to go over your problem areas.
I think you should then spend another week memorising the atar notes lecture slides. These are a great baseline. You can add extra notes to these later.
Then start on checkpoints questions as soon as possible. Past VCAA questions are in my experience the most helpful resource.
Hope this helps, and good luck!