Hi Nicolle,
Just to confirm what Wahm922 has stated, it is the presence of the store window inside the template that is causing your sizing issue.
We do our best to give users all sorts of templates all of which will resize according to how the inner content is laid out and the size of the browser window, there are very few templates that we provide that will not collapse down to 600 pixels wide as long as the inner contents does not extend beyond that. In fact, as an example, in the listing link that you provided the original template was designed to collapse down to to around 200 pixels wide if there is no content inside of it.
Take the store window out of the template and you will notice the largest element in your listing is the photo of the neckline on the shirt. Beyond that there is only a small amount of padding added to keep the pictures off of the border of the template itself.
Best of Luck,