Quote:
Originally Posted by e_mortal
Then I tried your other suggestion, changing the size dimensions around and the orientation, and that has worked  I'm glad to be able to do so but it's annoying why I can't fix the original problem. |
But you have fixed the original problem. Look back at your screenshots and you'll see the clues were staring you in the face from the start.
The ruler showed you that your "printable area" was roughly 7.5cm wide. You already knew that your margins were 1.27cm, so roughly 2.5cm in total.
7.5+2.5=10, so it was clear that the printer expected the paper to be 10cm wide.
Given that paper sizes are usually set in portrait orientation, and that switching to landscape orientation means turning the paper through 90 degrees, it is clear that the printer understood your paper had been changed from 21x10 to 10x21, so changing the way you set the paper size is the obvious solution.
If you want a permanent fix, ditch the HP printer.