Well, this is exactly what I did.
I had a 90. Yes, that's right. Then I did a Communications degree, and absolutely axed it. Got into law, graduate entry. Now I'm doing an LLM.
There is a future out there, so long as you bust your balls - no slacking off like you did in school ;D
I wouldn't worry. If you don't get a early Feb round offer, then just accept the best offer you got.
I hope you didn't just apply to uSyd and uNSW. If you get top marks at a second tier school, you can still go places.