enlarge and print photo

The zoom slider will just change how you are viewing a photo. It will not modify the photo itself.

You can set the print size in the Print Dialogue.

• Select the photo in Photos.
• Use ⌘P to open a print dialog.
• Now click the Custom layout and specify the dimensions of the printed photo, like this:

Enlarge? What size is the image now? What size do you want it to be?

Print: have you tried command-p, or File -> Print like every other app on your Mac?

You're welcome 😊