The IRS will continue to make stimulus payments until February 5. This is happening to a lot of people. If your return should be rejected when the IRS opens on February 12, then you can correct your taxes and resubmit.
But if your taxes are accepted, the IRS will have a procedure to resolve this. We do not yet know what they will do. If they do need confirmation from you, they will notify you.
You can cash the check and spend the money.
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