Scaling can happen in the PDF viewer or printer driver. Fit reduces the whole PDF to the printable area, and a paper-format mismatch can trigger another resize. Borderless printing may enlarge the image and crop its edges. Check these settings separately rather than changing the photograph dimensions to compensate.
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.
Before you print
Use Actual size or 100% in the PDF print dialog. Match the paper format and disable any further resizing in the printer driver. The preview shows the PDF layout, not a guarantee of your printer’s printable area. Start with ordinary paper and measure before using photo paper.
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.
Epson: Why a printer changes photo dimensions