Stretch a page to fill a full half of a page when printing two pages on one

I am trying to print the Swordfish Islands Worldbuilder's Print-It-Yourself Zine using a Canon MFW232W LaserJet Printer from Pop!_OS 21.08 from either Evince or Okular PDF viewers. I can get the pages to print 2 per page horizontally, but the pages do not seem to fill the whole half of a page. I don't think I did the correct sequence of configurations or buttons to get it to work. Would anyone have any advice on how to achieve this? The edges show where I am trying to make the pages expand. If this is the wrong StackExchange group, let me know.

Question by FilBot3 on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.