I'm not sure what you are referring to when you say an extension on your stimulus.

This link continues to be updated as information becomes available.  This information is provided by the IRS - Third Stimulus FAQ 

Hello, good morning.

My problem: I successfuly filed my returns on Saturday. However, I soon realized I had made a mistake. Since my returns were accepted I tried to Amend, but I had no success.

I decided to refile from the start.

I have updated my new return, but I did not send it in as yet, waiting to get some guidance.

Could you please help me?

Thank you, [Removed PII]

If your return has been accepted by the IRS, you cannot submit a second tax return. You can follow through to amend your tax return for errors or omissions, however, if you are amending to change ONLY your stimulus payments, then stop.

The IRS has made it very clear by stating they do NOT want any amendments for stimulus payment changes.   

• IRS Topic G: Correcting issues after 2020 return is filed 

The IRS is making the necessary changes, do NOT amend for any mistake made when entering your stimulus payments.

[Edited: 04/03/2021 | 6:55p PST]