the bottom of our grade shouldn't affect you too much, cos when they moderate the marks it isn't just your rank that determines the internal mark, but the differences in marks i think. from what i heard the top 80 or so were only separated by 8 marks... i'm not sure how true that is, but i think the top half are more bunched together than the bottom. anyways your mark is more likely to be pulled up than pulled down, unless that bos bitch lied to me about moderationhahahah i just hope we have enough guns up the top end like you, khfreakau and tambam to compensate for people at the bottom..
if you really want to try to work out external marks, use this thread: http://community.boredofstudies.org/showthread.php?t=254120
just compare trial marks to their scaled marks and you can work out your hsc marks, then put that into an atar calculator (that's what i did after our trials )