If your ATAR is strong enough (like 99+) and you redo the UMAT and get a reasonable score, it might be easier for you to apply as a recent year 12 school leaver than a transferee. The reason is for courses like law (no idea about medicine) in USYD, 30% of the intake is for transferees. Whereas 70% is for recent school leavers.
So if you are competitive enough for the 2010 Year 12 cohort, I would stop uni, and take a GAP year in Europe. But unless you really can excel in Bach of Science, then go ahead. That being said, if you really want to get into medicine you will push yourself to get that 6.5-7.0 GPA. So taking the transferee route is not impossible (I'm an law transferee example too)
I had a friend who got 99.10 ENTER and didn't get an offer for medicine, only for Arts/Law at Monash. She redid a few of her Year 12 subjects like Chemistry, Methods and also the UMAT. Now she's in medicine at Monash.