Grab a textbook (or three), read a chapter then grab the sylabus and go through each point making sure you at least have some knowledge of what it means.
There are good chem notes on the HSC website at CSU or something. Theres a link from bored of studies. They summarise most of the dot points so that would be an OK place to start. Only I think they would be of best use if you already learnt the stuff just forgot.
Still its definatly not too late for the HSC exam and even if it was theres no point wasting any more time worying about it.