Tote Bag Dimensions
Society6 tote bags come in three sizes: 13 x 13 inches, 16 x 16 inches and 18 x 18 inches. So they're all squares, but on the Society6 website, each bags looks to be a slightly different dimension.
The 16" bag looks more like a tall rectangle, while the 18" bag looks like a wider rectangle. With the same uploaded image used on all 3 sizes, it'd be impossible to have a design that perfectly follows the edges of the product. But at least with my templates, you'll know how your design will look before hitting the Upload button.
Download the Templates
You can download these templates as PNG files which can be imported into any image editing software. Just place it on top of your design at a lower opacity (and disable it before you upload your artwork!)
Or you can download the Illustrator template below (May require version 17 or later).