ok, when you get your results, you'll get what's called the HSC mark (which is how the bands are determined).
50% of the HSC mark is your (internal) school assessment (which is moderated according to how your school does in relation to other schools)
the other 50% is your external assessment - made up of the PIP (30%) and the exam (70%).
So in a way, yes, the exam is worth 35% of the whole HSC mark, but how well you do in your internal assessment is judged by your relative performance in the external assessment, so it is pretty important.
In other words, do your best