If you messed up big time, or you don’t want to proceed any further, and want to go back to the design as it was last saved, then we’ve got two ways to do that. The more obvious way is just to close the designer without saving, and reopening the design. Otherwise, you can use the start over button located under the more tab in the design center.
To completely clear your design/canvas, click on “Clear Canvas” instead. This button will remove all items appearing on the currently selected side of your design (front or back side). This is only if you truly intend to ground zero your design.