Nothing there indicating directly what is buggung, but two things might have solution.
First is that full page photo might strecht the image to be as big as possible.
What other options are there.
Second might be hiding under the options. Mind sharing what is under there.
We are looking something that says "Fit to page" ("Fit picture to frame" might be that) which must be off, and/or scaling which must be 100%.
Actually third possibility is that the cover has wrong dimension (I don't remember correct ones right now) or DPI (which should be 300, some rare ones have).
Check that in the properties or by opening it in Paint.