Your UCAT is really good and you might end up getting an interview at Western Sydney uni or Newcastle with those marks. If you end up getting an offer then it's all yours to decline. Probably best just to keep trying for now since you have quite a good shot at getting into med - that way you at least get some closure, rather than facing regret next year because you didn't apply. WSU need ~93.5 if you're from GWS so just keep working on your ATAR if that's something you want to consider. If you don't get in, it is what it is :/
It's much easier to go from med -> engineering than engineering -> med. It's probably easier to get a taste of engineering whilst you are in med school (just pop into their lectures. Biomedical engineering seems to combine the 2 - have you thought about that?
Also regarding working hours etc - if you love a job enough, it won't matter to you. Not too sure as I'm not a medical student, but I don't think it's repetitive as you see new cases in the hospital everyday. There is a lack of flexibility in school as you have to do a certain curriculum, but there's room for choice in your electives and future specialty.
If you're worried about having to commit to med, this guy left med school after 4 years to become a bus driver and he's loving life! It's definitely okay not being sure what you want to do and it's definitely normal to change things up.
https://medstudentsonline.com.au/forum/threads/from-medicine-to-trains-cathays-journey.35605/