Narrow container, site displaying at only 845px wide?

Hi Mark, and anyone else who may be able to assist.

I recently (finally!) upgraded to the responsive DT theme. Upon activation the container of my site is very narrow and looks nothing like the nice wide demo (and examples in the showcase folder).

Can you please take a look and let me know why my site would be displaying so narrow?

https://weddingswhitsundays.com.au/