The IRS will correct incorrect stimulus amounts claimed on an income tax return, but they will not add a stimulus payment if you did not include anything on your original return.
Check your Form 1040. The amount of stimulus included with your refund (called a Recovery Rebate Credit on the return) appears on line 30. If the line is blank you did not fill out TurboTax correctly and need to file an amended return.
How do I amend my 2020 return?
If there is an amount on line 30 and you did not receive $1,200, then you may have made a mistake when completing the stimulus screen in TurboTax. The IRS paid out the stimulus so they have records of how much they gave you.
If you think the IRS made a mistake, you can call TurboTax and ask an agent to look at your return.
The IRS says: "[If] you didn't claim the credit on your original tax return, you will need to file an Amended U.S. Individual Income Tax Return, Form 1040-X. The IRS will not calculate the 2020 Recovery Rebate Credit for you if you did not enter any amount on your original tax return.
You can use the Interactive Tax Assistant, Should I File an Amended Return?, to help determine if you should amend your original tax return.
2020 Recovery Rebate Credit — Topic G: Correcting issues after the 2020 tax return is filed
