To save the artwork you have created using the online editor tool, simply click the "add to cart" button. This will allow you to edit your artwork or place your order at a later time.
To edit your saved artwork, click on the "Edit" text below the product details on the shopping cart page.
See screenshot below:
The Box Preview button allows you to visualize the box in 3D, but not to edit it. Double click on the box to see it open and close.