Yeah, you should still try. If someone bombs out (ie. gets the worst HSC exam mark), their mark will most likely be an outlier result, so it won't be calculated with your cohort, and calculated separately. As long as you're somewhat with the pack, you shouldn't really give up. Also, if you do amazingly well, your mark would not correspond with your rank, right? BOS could also consider this as an outlier result, and calculate you separately. It has happened numerous times before, so there's no reason why you should give up.
Now it just means there is a lot of pressure on you to do well.