You have the option to include a bleed, which customers have the choice to include in their downloaded file.
To include a bleed in your design, open the Info tab and scroll down to the section Design Settings>Show Bleed. The bleed will display around the canvas (separated by a dashed line) for both you as a designer and for customers when they go to edit. By default, the bleed size is the print industry standard size of .125-inches on all four sides of the design (for a total of .25-inches added onto the length and width of the finished design size). You can also set this option up in your account Settings>Listing and Design Settings (upper RH side, under seller profile) so that the bleed is included every time you create a new design. (Please note that this will not change the settings in existing designs.)