The printer settings on your Adobe Reader app might have a different set up from your QBO Desktop app, bacmac15.
QBO uses the Adobe's settings when printing a document, especially if you're getting a PDF copy of your transaction right before printing it. This article from Adobe's support site will walk you through the steps: https://helpx.adobe.com/acrobat/using/using-pdf-printer.html.
You can also reset the QBO app data in case it keeps reverting back to the default paper size . Here's how:
Then, log back in and print a transaction to check if everything is already working fine. Please keep me posted if you have other questions.