TurboTax instructions do not do a good job of informing users that they need to make a backup copy of their return before they do any amendment. If you do not have a backup copy of your return all you can do is stop the amendment and then undo any changes you made. I believe the software should be altered so that a copy of the original is saved when a user begins to amend. In your case you may have to start over from scratch, then mark the return as being mailed, but do not mail anything. Save a copy of your work. Then go through the amend process again.