Hi,
Once you have set the prints sizes using the "Zebra" button either on a thumbnail or at the bottom of the page preview, click the Save icon at the bottom of the print properties dialogue window.
See attached screen shot.
NB. this saves the print size so if a different page size is used the number per page will change.

You can save and recall a Print Setup using the file menu which saves everything: "A printer setup file contains all print related settings such as driver settings like page size, paper type,print quality, etc. and also Qimage print related settings like the printer profile, margins, etc."
Terry