Crashoverride you are wrong ( I say that in the nicest possible tone)
Your HSC mark is an average of your external mark and your internal. Your mark is the mark that the person who came second in the external at your school got. And if you got the highest mark, that would constitute for the internal mark of the person ranked first. Eg, if someone, say Laurie, came first in your internal ranks but second in the external exam at your school, then he would get your external mark and you would his. This said I'm assuming there isn't a great gap between both your internal marks, if there is the BOS does some weird scaling which is unpredictable.
Edit: In summary, don't think it's possible to top the state if you didn't come first. Unless the average (aggregated) mark of the top two people are the same. Unlikely, but you can always live in hope