Adjust the artwork for your specific print size. When you print on canvas, the canvas is stretched over a wooden frame and the sides will cut into the design. Depending on the design, the size of the print, and material, extra content needs to be created so the print will not cut into the design.
For your reference, in photos 2 & 3 you will find how the photo will look without extra content created. In 3 & 4 the file had extra content created, therefore the result is perfect.