listen to these people. your yr 11 marks count for ZERO of your HSC/UAI. i know teachers may look unfavourably on it, but i see no real reason why you shouldnt just start the yr 12 course now. grab a textbook and start reading/writing some notes for it.
i've found that we have really had to rush the last two topics because our teacher spent so long on the first two. perhaps you'd be better off starting with one of the later topics (either the option or I2I).
one thing to be careful of however is if you're looking to apply for scholarships - they will often ask for yr 11 reports too...