At tis point, you will not be able to correct your return because you have already submitted it. You will need to wait until the IRS accepts your return and then prepare an amended return to pay back the $600 credit you received. This year, the IRS are not accepting electronically filed returns until 02/12.
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New - If you filed and claimed the Recovery rebate credit but already received the full Stimulus payments you can call it back and update your return so it isn't delayed