I completed my taxes, and opted to mail them in. I have not mailed them yet. I have since received an amended document. Can I change my return since it had not been filed

Yes, you will need to get back into your return through a back door however.

Log into your account / return

Click on "Tax Timeline"

look for "other things I can do" on left side or at bottom of page.

Under "other things I can do" choose ADD a STATE (this will get you back into your return).

Go to appropriate section and add the document.

Do a "review" to make sure everything is correct

Click on File Tab at top of page.  This should step you rest of the way through printing.

If for any reason it does not step you through printing, go to
My Account > Tools > Print Center and try printing from there.