Hey Zoe!

Not sure if you've found a solution to your problem yet (hope you have), but if you haven't then I'll try to help.
1. Consider your study methods for other subjectsThink about how you study for your other subjects whatever they may be. Try to apply these methods into your bio study.
2. Study timetablePeople might have told you to make one of these since it helps you to organise how you study. It can help you figure out how much time to dedicate to study for bio. To make one, first list all of your subjects in order of difficulty to you. Then figure out how many hours you have in your week to study. Then distribute the time you have between the subjects you do, dedicating the most time to your most difficult subjects. After this you can write up a table or spreadsheet with the hours of each day and slot in the subjects into the hours you have available for study. Make sure you also include leisure time, this is just as important as study time because it gives you time to relax and process what you've studied, how much time you dedicate to this is your choice but don't go overboard. If, like me, you can't be bothered making one that's fine, this is only a suggestion.
3. Find your method of study based off the way you learnIf you learn better from pictures, draw posters with diagrams about processes you learn in bio like the cell cycle or steps in cellular respiration. If you prefer reading, read your textbook, or sheets and notes your teacher gives you and highlight. If watching videos helps you learn, Youtube has some nice channels that explain some the tough topics in bio like 'CrashCourse'. Maybe saying things out loud will help you out, getting a friend to test you with flash cards can help to remember definitions or basic steps to processes.
4. Learn from your mistakesGo through your SACs and write down what you got wrong or could've done better in. Doing this may bring back awful memories and make you feel bad but it'll help you not repeat your mistakes and it helps you figure out what specific areas you need to study.
5. Ask questions and use the resources you haveYour teacher is there to help you out and so are the people of ATAR Notes, so use these resources to clarify issues or find extra work to do. Like Sine said, bio questions are all about application so doing practice questions or extra work pays off when it comes to SACs and exams. These resources can be past exam papers (just looking through the unit 3/4 ones can give you an idea of how they ask questions), textbook questions and (not sure if you have these or not but) Biozones. Biozones were one of the items on our book list for bio and they give you nice application type questions and often don't . Friends and family can help out too, you can teach them, as suggested by skybluemaniac or they can teach you if they have background knowledge on bio. Also ATAR Notes has a thread with lots of study tips for bio (
Biology Resources) which are probably more useful than mine

Those are some of the tips I can think of. Biology isn't the easiest subject on the planet but it's not impossible to succeed in it. If you want to improve you will have to dedicate time to developing these study habits but luckily for you it's not too late because you still have time before unit 3/4 starts. I'm not an expert and this is one of my first posts so if anyone thinks I've given some not very great advice or someone can elaborate better on this, please do! NOTE: these are only suggestions and they might not be for you so ask other people for better advice. Good luck, Zoe and DON'T GIVE UP!

(sorry for writing so much, I got a bit carried away)