I find tools et c. in The Gimp far from intuitive! I have printed the Gimp manual from the command line, and also viewed the large User Manual in the Website. I can't find answers to these problems, notwithstanding the apparently helpful "Gimplite Quickies".
I have edited an image (jpeg) in Gimp to a print size which will fit into A4 (both height & width) and saved it. Then I open it with Image Viewer and click File/Print, and then on the cups screen select Preview. Preview opens in a screen headed: "PreviewQ7SY9T.pdf" and shows image too wide for page.
BTW, after some changes in The Gimp, it reports failed to save - something like "too few lines scanned" although an apparently full size file appears in the destination - but won't open. . After other changes it says Export first - then goes on to save.
I shall be grateful for any hints toward progress. At present I feel like a "bear of very little brain" to quote A A Milne.