don't know what to do and parents will kill me...

[froths]

I haven't had great Internet connect the past two days (in my cousin's apartment in Singapore), so I'll give you my take now.

Repeating year 12
I don't think you should do it, but for different reasons than the aforementioned ones. Firstly, please note that I don't have any disrespect for people that repeat year 12. With no disrespect to those institutions ( I realise they have their own purposes), I don't think CAE or RMIT are great environments if you are aiming for a high ATAR. The majority of the students in those institutions are high school drop-outs or adults. They are more doing VCE for the purposes of attaining an educational certificate rather than aiming for a high ATAR. Furthermore I've heard that at at CAE, only about 45% of the students receive atars of 70+. While I'm definitely not implying that you'll most likely get an atar below 70 seeing that you went to Macrob, my point is that it is extremely difficult to score in the high 90s ( not implying that it would be possible easy to do so in a good school, but it's so much more difficult in RMIT/CAE). For the majority of subjects, the teacher support is horrendous. The effects of this may not be as pronounced in maths/science subjects where an intelligent person could complete the course on their own, but in humanities subjects, teacher support is pivotal for the most part because they have special assess to various material and they can critique your work. This is why the top scores in humanities are dominated by students in top private and selective schools. You also better be rank 1 there with the atar you are aiming for .

Having done my VCE at TAFE this year I'll second this. It's different to a normal school and if you lack motivation - as the OP indicated - you'll struggle in an environment commanding much more independence and self-reliance. I obviously can't speak for CAE/other adult institutions, but here many rocked up for the first few weeks of classes before disappearing and quite a few didn't sit exams. Most teachers are helpful but only to a certain point - they don't bother chasing lazy students to attend classes or complete work. SAC averages + the median ATAR are also quite low and so you might experience the rubber-band effect of a laissez-faire environment.

Likewise, repeating it at school means you miss out socially and experience the stress of exams/SACs again. I doubt your ATAR would change much. If you're really hell-bent on looking down this path, perhaps it might be worth just completing an extra subject or two via Distance Ed or similar? It might improve your results a bit without necessitating the time and effort of a full 4-5 subject load, meaning you can also do uni/work/TAFE/whatever in the meantime.

Best idea IMO is to look at pathways/courses offered by other unis which might allow you to transfer with good enough marks. Sweat over what's already been done and you'll find yourself in a bigger rut.