Chem for biomed is a hard subject, but it is definitely possible to pass even if you're shockingly bad at chem. For what it's worth, I got a 31 in VCE chem and got through Chem for Biomed, so you can too! Don't worry too much about the MST, because it is worth so little (I think only like 2% of your overall mark). That being said, you'll need to do some revision of thermodynamics and I'd advise you to repeatedly go through the tute question booklet and try to master the problems in that booklet, because they will put you in good stead for the exam. Go annoy your tutor with 100s of questions, because they're paid to help you out.
They've actually changed the ordering of the course a fair bit (we did thermodynamics way later on) so that might explain why you're finding it a bit tough. I personally thought the organic and biochem that you do later on was a lot more interesting and easier to learn, so things might look up. If you think you're struggling a lot, use the Chem CAL tutorials on the LMS for the actual course content. They're really helpful and can lift you up to the level where you want to be. My #1 piece of advice: don't give up now, because the workload will keep stacking up and you'll find it increasingly harder to catch up the less you do now.
Best of luck.