The bias I cannot comment on but if you really felt that way, maybe you should have discussed it with the head teacher, deputy or principal. The teacher is accountable to explain the difference in marks and how you could improve them.
As for the marking, teachers will be looking for a variety of things in marking not just what happens in the HSC. Once again the assessment covers a lot more skills and other aspects that are not examined. This is why in science only 50% of your assessment is suppose to be tests or exams. You can't do a speech in a HSC exam but it is a skill that your assessment may cover.