When you first add "doing an amended return", then it should show the original numbers on the 1040X column 1.
THen, if you add changes, the corrected return will show in col 3 and the changes on the line numbers will show in the center column.
Here is some additional information for you:
First, make sure you really need to amend and that your 2020 return was accepted in TurboTax Online or paper-filed through the mail. You can't amend a return that hasn't been filed yet.
When you're ready to amend, find your situation below and follow the instructions.
TurboTax Online
TurboTax CD/Download
Related Information:
IRS Wheres My Amended Return
Please refer to the additional information at the following link:
How do I amend my return