I have the same problem. The scaling feature is grayed out, regardless of the printer I select and all of my printers are capable of scaling. Also, the printout both on-screen and on-paper is in the upper right 1/4 of the page and unreadable. Does anyone else have this problem? This problem started with Q-2018, I never had it in all previous versions.
Verify that your printer's System Properties are set to 8.5*11 standard paper and NOT Auto-detect paper or photo-print or something similar.
I remember some old posts that attributed the little page preview to a screen rendering issue, but if you say that it also prints on paper at reduced size I'm more leaning towards a printer setup issue.