On the 2020 tax return, under the Federal Review Section, TurboTax asked the question "Is this what you received "the stimulus payments of $2,400 and $1,200. The option was to select "Yes" or "No".
If select “No", there were 2 options to type the 1st and 2nd stimulus checks amount we received.
No, you shouldn't amend to get more stimulus payment. Based on what you said you received $2400 and $1200, which is the amount you should have received.
You should have answered Yes, that you received those amounts. Instead, you said No and then entered the same amounts. That isn't the way it was intended to be answered, but it gets to the same point of saying, "We received $3600".
By going back and answering No and $0, it looks like you are saying you never received the $3600 at all, so the program thinks you are owed $3600. That is not correct.
The bottom line is what was filed on line 30 for the Recovery Rebate Credit. If you got the full Stimulus amounts then line 30 should be 0 or blank. If it is blank it worked right. If you have an amount you were not qualified to get then the IRS would have automatically adjusted it off your return and sent you less refund or a bill. They know how much they sent you. I wouldn't worry about it now.
Same thing for 2021. Did you get the full amount for the 3rd Stimulus 2,800 (1,400 x 2)? Make sure you don't have an amount on line 30 either.