Hopefully the IRS will catch it and add the second stimulus to your refund.
The IRS will calculate the correct amount of the Recovery Rebate Credit when it processes your return and make corrections. If a fix is needed, there may be a slight delay in processing your return and the IRS will send you a notice explaining any change made.
The stimulus money is not taxable income to you.
If you e-filed your return, you won't be able to change it. It's like putting a letter in the mailbox. You can't retrieve it.
If your return gets rejected, you'll be able to correct the stimulus payment and submit the corrected return.
If your return gets accepted:
Note: Generally, Form 1040-X, Amended U.S. Individual Income Tax Return, must be filed within three years of the date the original return was filed, or within two years of the date the tax was paid, whichever is later.