Need more info on "half the picture".
Do you mean that half the page contains the whole picture and the rest of the page is blank?
Or, half of the picture takes up the whole page thus needing a second page to print the other half?
Yes. Half the page has half the photo while the other half is blank.
Actually to be really clear only half the photo is printed on the page
while the other half is completely blank.
Do you have the paper size set correctly in the printer driver?
Do you have the cell size set correctly in Lightroom?