The center canvas does not look like a canvas. I spent a few minutes staring at it, wondering why there was an advertisement in the middle of the screen where I thought the canvas should be. It's really not clear.
The canvas is an orange rounded rectangle.. Seems like (1) the canvas should start out white instead of orange, and (2) the canvas should look more like a "canvas". And relocate the buttons in the 4 corners that obscure part of the canvas - those are really distracting.
Is there a way to specify placement on the shirt?
The tool to rotate, resize and re position elements is pretty, well, clunky. I'd push your developers to make the design elements directly draggable. It's probably more work, but substantially more intuitive for the user. And there should be some kind of feedback that (a) the elements are clickable, and (b) which element is selected. Also, the "spin" functions are hard to use. Elements seem to rotate about the left bottom corner rather than the center.
One of my pet peeves is buttons that don't act like buttons. There should be some kind of visual feedback when you hover over a button or other clickable element (color change, cursor change, underline, etc).
Chris