It worked fine for me.
Did you click on how many years you want it for (where it says 1, 3 and 5)? For some reason, even if you don't select any, it still directs you to the cart.
I'm not sure if you can delete it. But all preferences before the course you were offered will be considered.
So if you were to rearrange your preferences so that the one you were offered is last, all your previous offers will be considered.
I agree.
Despite having not studied law I think as long as you've got the motivation to work hard, you can excel in any course. Besides, look at what you've achieved already. Great job!
Ahh looks like they moved it here:
http://www.smh.com.au/national/education/choosing-art-theory-hsc-top-performer-turns-back-on-the-law-20140116-30xts.html
I think the concepts in Chemistry are generally harder to grasp than in Physics and Biology. Despite this, the sheer quantity of content in Biology will probably compensate for this.
I found Physics to be somewhere in the middle.