How to print a PDF or image at full width of the printer paper?

I'm attempting to send images to my ZQ520 printer to print. They end up printing, but they're always printing at a much smaller scale than they need to be. The image is shrunken down to about 2/3 the width of the paper. Are there any tutorials for configuring this?

I'm testing this using the DevDemos app from the Zebra GitHub account. When launching the app, I go to "Image Print", choose "PDF Print", and it prints the PDF, just at a shrunken size.To get PDFs (and images) printing at full width of the paper, is that something I need to change in the Objective C code, or a configuration setting on the printer?