I think the instructions above the duvet cover prices say the image needs to be 5000 x 5000 pixels in over to cover the whole duvet. The largest my camera goes is 4608 x 3456, and those fit nicely with a colored border. If the image is too small, I just don't offer that one on a duvet. It won't look nice and stretching it to make it bigger would destroy the image clarity. If you can get your posted images up to the 5k minimum, that should take care of it.
