“The ai told me it’s right” is actually probably my biggest problem with AI being freely available. Yes I know karens existed before AI but even then I feel like the excuses were more… thoughtful? IE my dad is a designer/it looks right in the photoshop preview whatever.

Well, yes - those AI tools output images in aspect ratios which are not those of a typical sheet of paper (16:9, 2:3), which indeed wont't match. "Inches" etc doesn't matter.

You just need to offer the customer either the options of scale-to-fit / fill / stretch (white borders / crop on two edges / stretch), you probably already needed to do that before AI (such as people wanting to print letter-size documents in A4 land).

You dont have borderless printers there? Scale to cover full page and go!