Hard to say with IT. There are a collection of very strong students at the top end (like with any class), but there's also a very large gap between high and everyone else (anecdotally).
For a 50, you want:
- Rank 1, or the highest you can manage
- a reasonably high SAC average
- an excellent exam score
To prepare for the exam, I'd recommend first and foremost just going over your notes (or if you don't have any, now's a good time to make some). Get an idea of things you don't know so well and go back and learn them properly. If there's nothing that stumps you, try a practice exam, timed and note free. If nothing gets you still, just keeping working on practice exams until you run out. Something to keep in mind is the general lack of practice material for SD; there's 9 exams from the VCAA and only a few companies offer them, and you'll find you probably have to purchase them out of your own pocket because most schools wouldn't bother with such small classes. Doing one a week starting now will leave you a whole week or so of leftover time, which might work for you, or it might not.
Reference material probably consists of your textbook, your teacher,
vceit and here's not a bad place to get your questions answered. You're certainly on the right track to scoring very well in Software.