I'm in a less than stellar agriculture class, who really don't care about their HSC or school in general. My overall prelim mark was 92%, while the 2nd ranking student's mark was 68%. Will this drag my mark down when it comes to HSC scaling?
As long as u come first it won't affect the mark you can get. Since the first ranked person always gets the highest assessment mark = to the highest external exam mark even if they don't come first in the external exam. In your case you will probably come first anyway in both. The bad thing though is that practically all your mark is decided by how u perform in the external
If you come first in all your subjects, then there is nothing to worry about in terms of your cohort dragging you down since your school assessment mark will always be the highest HSC exam mark achieved in your class (which will probably be you if you're first anyways).
However, likes Jazz said, this does mean that your HSC is practically entirely determined by how you perform in the HSC exam - just make sure you stay healthy before the exams so you can think clearly.