Enough thinking about UAI's, i have an option that you might want to think about.
The University of New England (in Armidale) has an Early Acceptance scheme where your entry doesnt get based on your UAI,but on a recommendation from your school principal. So if you think youre not going to achieve the desired result in the H.S.C it may be an option you can look into. Your school career advisor wouold be the best one to ask. Its what i did!
See I got high 70's in the H.S.C (which was crap cause i thought id do better lol) but my UAI was scaled down because of the school i went to (Good old Macquarie Fields for you lol) and only came out with a UAI of 55.75, which cut my options down to living on the dole or doing hairdressing at TAFE lol, no chance of the Uni degree i wanted. But because i went through the Early Acceptance scheme, just as a back up, i got into 2 different courses and was able to choose between the two.
You may not want to move away from to home, to Armidale but i did, lived at a college (GO EARLE PAGE!!!) and had the best time of my life
Just some choices for you (hope ive been some help!!!)