1. Use the "Upload your print" option to access it. We will be rolling it out also for "Design your print" at a later stage.
2. Once you have uploaded a file you will get the option to Mirror sides. When you select it we will fit your artwork to the front side of the canvas and then mirror the edges and bleed from the content on the front side.
Note: This feature works best when you have the same proportion of the artwork as the canvas. E.g. if you are printing a horizontal canvas then use a horizontal image.