Glad it’s working OK for you now.
The Product Template ID 840 is actually an outdated template from the original Flash app, it has an issue with the mask that is outdated we can correct. The product actually allows design in the outer section of the frame, not the inner picture area. Is that what you want?
If you want to set up a bunch of blank sizes, you can use the plugin TM Extra Product Options to set up “width” and “height” fields for one product. Then, you can use that product to set various sizes, click through to the Customizer, and copy those links as a way to generate dynamic product templates of various sizes and options.
If you don’t want to go with blank sizes from the above method, you can have specific templates made to match your exact print specs, with graphical templates made for you and integrated with new template IDs by our team. We have to do those manually in house. You can purchase that service here through our website for a one-time fee per template, and you can keep the IDs private to your site once they’re made. New product template creation services can be purchased here: https://mystyleplatform.com/product-category/customizable-products/