When you prepare your 2021 tax return next year you will be asked if you received the 3rd stimulus check. There was no place to enter anything about the 3rd stimulus check on a 2020 tax return. And if you made a mistake on your 2020 tax return pertaining to either the 1st or 2nd EIP payment, the IRS has been cross checking every return with an amount on line 30 for those payments, so they will catch mistakes made for the 1st or 2nd payments.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**