i think it is possible,
but you're gonna need to blitz your trials and HSC, now when i say blitz i mean top 5 in all your trials and even better in your HSC,
now you say "i hardly opened a book before my half yearlies" is what im worried about. Think about the other students. They already know the first half of the course much better then you AND they are learning the new stuff too. If you really want it then of course yeah you can get it.
your school rank isn't too bad. you have to set up a timetable and be as strict as possible with it. no breaks where they aren't needed, no naps when you're tired, no distractions while studying. sleep 8hrs a day (you need sleep to study) drink 2 cups of water when you wake up (helps studying heaps) and try to minimise time wasted so you can study well such as time wasted on transport, lunch,recess, waiting.
GET RID OF YOUR SMARTPHONE,
when you study, dont have your computer on, all you need is a pen, paper, textbook, lights and a desk, no phone nearby no computer nearby, set up a place to study.
that all being said, it's possible for you to achieve it, even if you don't it builds character and discipline which you need if you want to be successful in life
as others have said just transfer if you don't get the atar you want
"if you can't squeeze through the doorway, you can always climbs through the window"
i realized all of this probably just before half yearlies and i blitzed them setting myself up for ATAR around 98.00
i recommend that you spend some time alone maybe as you try to sleep or when you exercise, anytime when you can gather your thoughts (in the shower) and have a long hard think, then promise yourself that you're gonna give it your best shot.
GOOD LUCK, AND I HOPE YOU GET WHAT YOU WANT!