Hello! Here's my entry for your contest. Since almost everyone is using the opera house, I used the Sydney Convention Centre for a change since the convention will be held there and I just added a map of Australia at the background. Hope you like it.
Perhaps the Harbour Bridge? - it will link it better to Sydney (as not many would know what the Convention Centre building looks like), and it's a little busy with the map of Aussie.
And then perhaps flow the text 'We're On A Roll' over the top of the bridge?
Australisian and date text and layout are fine.
Perhaps some rounded corners to lift the badge effect to something a bit more dynamic?
Can you then add a 'gloss' or 'plastic wrap / highlight' effect to all that for a bit of polish?