Email: hello@printsized.com
This is the most valuable report there is, and it will be fixed quickly. Please include the photo size and paper size you chose, what the print actually measured with a ruler, and which PDF viewer and printer you used. The scale setting in the print dialog is the usual culprit, but if it is a genuine error in the tool it needs correcting immediately.
If you regularly need a photo or paper size the tool does not offer, say which and where it is used. Regional ID photo sizes in particular are easy to add and hard to guess from the outside.
Please mention your browser, and whether you are on a phone or a computer.
This is a small independent site run by one person, so replies are not instant, but every message is read.