A tax return is not proof of marriage. Your marriage license or marriage certificate in your proof of marriage.
Download the PDF of your tax return and just print the pages you need using any compatible PDF viewer, such as Adobe Reader.
To access your prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/
Scroll down and on the section Your tax returns & documents click on Show. Click on the Year and Click on Download/print return (PDF)