Pages Document prints off-center

The flyer I am working on in a Pages document was made on a vertical, blank canvas. I finished the document and now tried to print it. The document has a yellow background which I centered as a square shape. Even though I centered the square, when the document prints I end up with a wider white margin/border on the right and bottom sides than I do on the left and top sides. I did not change any default settings. All margin settings on Inspector show 0. I am printing on an HP Photosmart Premium printer. Maybe it is the printer setting the yellow background off-center? When I print "borderless," the discrepancy disappears. Any ideas on how to center the background besides printing borderless? Please let me know. Thanks!