Basically, I agree with notthedevil. For WWI, you can honestly get away with a rather rudimentary knowledge of the content (and by that, I even mean get 25/25), simply because the examination content largely revolves around your ability in analysing sources. Although I would obviously recommend...
Some of the estimates given in this thread are way too harsh. Judging by ranks, course enrolments, etc. I'm quite sure I know what school OP goes to, and looking at the past HSC stats of this particular school, OP still is on course to (albeit barely) scrape a B6 in 2U Maths and an E4 in 3U...