Check the study design for Unit 3/4 Bio, it will show you every relevant area of bio needed for next year. In general it encompasses cell structure and function (membrane, nucleus etc), photosynthesis and cellular respiration, immune system (not really touched on in U1/2), cell signalling, genetics and evolution (how life changes over time stuff).
Unit 1/2 is pretty similar and 3/4 will feel like revision for a lot of it, you should focus on the concepts that you find difficult and expand on it more.
Also, ecology and anatomy are not really relevant to 3/4 bio so if you learn that this year then don't worry too much about it (unless if you find it interesting anyway).
Heres the link to the study design by VCAA:
https://www.vcaa.vic.edu.au/Documents/vce/biology/BiologySD-2016.pdf