I have just returned to LR after many years using Apple Aperture and am having an issue printing anything but a 4x6 print from the Print Module.
To print a borderless 4x6 print, I select the User Template for 4x6 print and - assuming first I remembered to crop the image to 4x6 - it fills the view and the printed 4x6 borderless paper.
But if I try to do the same with a 5x7 or 8x10, I get a small version of the picture (probably around 4x6 I guess). What I notice is that in the right hand set of adjustments under layout, for both 5x7 and 8x10 I see "Cell Size" as 4 inches by 6 inches. I have read the instructions in the help pages about how to change the cell dimensions BUT that only allows you to go smaller, not larger.
How or what am I missing to print larger prints? I have not changed any of the user template printing settings (the ones you find on the left hand column) besides my 4x6 borderless one.
Have you chosen the right paper size in Page Setup?