Hey there,
In terms of your question regarding specifically the Bachelor of Science course, I did some research for you.
For Melb Uni, you need at least a 25 in in
one of Biology, Chemistry or Physics, so all good there
For Monash, you have more of a range: a study score of at least 25 in
one of Biology, Chemistry, Environmental Science, Geography, Mathematical Methods (Any), Specialist Mathematics, Physics or Psychology, which is really great for you!
Many, many people have found Units 1/2 of chem very dry and boring, and say it got a lot better in 3/4. I'd definitely recommend trying to stick it out for the rest of the year and definitely as everyone said check out the study design as that has all the useful, up to date info and talk to your teacher about how you feel and get their views. Many people advise you to always keep chem handy but there always many pathways, it just may be more time-consuming to get to your desired course.
Also, you can sit UCAT in Year 12 and any year after that which is great. Hope I've helped