Enable the 20 mm calibration square, export one sheet and print it on ordinary paper. Measure between the square’s line centres in both directions. Then measure the photograph rectangle. If the square is wrong, investigate print scaling before changing the layout.
The 20 mm scale check
The optional control square is 20 × 20 mm. It reserves space at the bottom of every sheet, so enabling it may add a page. Compare both measured sides with 20 mm. For example, a 19 mm side indicates 95% scaling. Do not enlarge the photo to conceal a scaling problem.
Find the cause
First compare the PDF paper format with the loaded paper. Next check scaling in the PDF viewer, then in the driver. If only the image edges disappear, inspect crop mode and borderless expansion. If only part of the sheet is missing, check the printer’s nonprintable margins.