Our school isn't studying Nineteen Eighty Four, which I think is a pity because I quite like it. Keep in mind, I haven't read it in a while. I would personally pick Topic One, if I had to write on one of them, but this is really only because I don't think I have a thorough enough knowledge of the text to write on Topic Two.
I assume your contention is that you agree with Topic One -- correct me if I'm wrong here, of course. It DOES say discuss though, so I think that you could also insert a paragraph that goes AGAINST your contention, but then at the end justify it by saying how it's all wrong and that it is indeed a warning. You could probably spend an entire paragraph talking about Orwell's definition of dystopia, and use quotes and text references to back it up. Then I'd probably devote another paragraph to the extent of the corruption in that society... again using text references and quotes and so on... I do think that you're on the right track, though.
For topic two... before even starting it you need to figure out what Orwell's message is, and if you thought it was effective or not. If you did, then use the essay to explain why, and if you didnt, then, again, use the essay to explain why. Hopefully you think it did but only to an extent, then I'd probably alternate paragraphs for and against the clarity of it. Beyond that, I can't really go into much detail -- sorry -- you really CAN tell I haven't read it in a while.
To prepare for the SAC, I'd personally get a quote list -- and memorise key quotes to use in the essay. Every text has these, 'must-have' examples that need to be used no matter what topic it is. Good luck tomorrow.