This might sound a bit slack, but you can't really blame your teacher for you failing. They are a teacher because the KNOW what they're talking about. Leaving it this late to say "wtf? i know nothing" is irresponsible.
You should talk to your teacher and discuss what you should do. Really, you should've done that when you didn't get anything in class. They're not mind readers sadly, so you're gonna have to tell them you're struggling. If you don't get a certain concept, ask for help.
Admittedly, year 11 marks don't carry over so you're alright on that. However, the stuff you learn now is the foundation of the HSC course. If you're intent on keeping the subject (implying you either need or like it), you should've put the effort in and motivated yourself.
All you can really do now is teach yourself the content, summarise a YEAR'S worth of work, and cram like no tomorrow. It's gonna be unpleasant. I really hope that you're exaggerating when you say you know 'nothing'.
(I'm not trying to be nasty, but hopefully you understand the point.)
