You cannot make changes to a return that is in pending or to a return that has just been accepted.  

We do not know if entering the wrong stimulus amount will delay your refund --- or for how long if it does.   The IRS has not offered any guidance yet on how they will handle returns that have incorrect stimulus amounts entered.  We all just have to wait and see.  You are among many people  who were confused and entered incorrect stimulus amounts, or who filed early and then received a check.   

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How do I find out about me federal refund 

IRS Where's My Refund tool provides current information about IRS processing.

If you have not received one or both of your stimulus checks, you will receive your payment in the form of a Recovery Rebate Credit on line 30 of your 2020 Federal tax return when you file.

If you have e-filed your 2020 Federal tax return and the tax return is accepted by the IRS, you will have to amend your 2020 Federal tax return and correct the entries and calculations to receive the Recovery Rebate Credit.

In TurboTax Online, you are prompted to input stimulus check 1 and stimulus check 2 information under Review down the left hand side of the screen.

You can access your stimulus check choices by following these steps: 

• Down the left side of the screen, click on Federal.
• Across the top of the screen, click on Other Tax Situations.
• At the screen Let’s keep going to wrap up.  Click on Let’s keep going.
• At the screen Let’s make sure you got the right stimulus amount, click Continue.
• At the screen Did you get a stimulus payment? you can update your stimulus check entries. 

TurboTax will compare your two payment amounts to the computation within TurboTax.  The computations within TurboTax are based upon the information that has been entered into the tax software.  If you are due an additional amount, it will be issued as a Rebate Recovery Credit (RRC) on line 30 of the 2020 1040 tax return.

See also this TurboTax Help.