Though never think that you're going to fail a subject, even if you think you haven't studied for the subject enough.
^^ Don't worry, you'll do heaps good, because don't forget, even if your school ranking isn't good, remember that you're ranked out of the whole NSW. Lol, I've heard about alot of previous people who actually studied up to 2 am before physics hsc exam once, and kept telling me that they failed..but they ended up getting 80% to 90% due to scaling as well...
So don't think about it, and try ur best, if you're worried, use next morning to do a quick revision.
Lol, like even right now I can't seem to sleep for some reason, though Ive studied quite abit.. XD