I honestly believe I messed up. I was so stressed when I was doing my taxes I couldn't think or remember anything. I know I didn't get the first 2 stimulus checks but I think I got the last one. How will I know if theres a problem with it? Is it gonna take forever to fix and resubmit and get my refund? Dang it!
If you received the 3rd EIP payment you should have received letter 6475 from the IRS. You can also check your own banking records for deposits of $1400 per person in 2021, or you can check your online IRS account to see if you received the 3rd payment.
https://www.irs.gov/payments/your-online-account
If you did in fact receive that payment, and you said on your return that you did NOT receive it, then there will be an amount on line 30 of your Form 1040. If you received the payment already---then you should not have an amount on line 30. The IRS is going to cross check returns---they know if you received the payment. If you put it there by mistake they will take it away----and that will delay your refund. You do not need to amend or do anything about this---the IRS will take care of it if necessary.
PREVIEW 1040
https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing
Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.
As for not receiving the 1st or 2nd stimulus checks---if no one could claim you as a dependent for tax year 2020, then you can file a 2020 tax return in order to get those payments----IF you really did not receive them. Again---look at your online IRS account to see if the IRS says you got the payments.
If you received the third stimulus but selected that you did not and therefore qualified for the Recovery Rebate Credit then the IRS most likely will adjust the amount automatically. Please see IRS Recovery Rebate Credit Q D2 What happens if I claim the incorrect amount? for additional information. If not then you will need to amend your return (1040X) and send the funds back to the IRS. Please see FAQ How to amend a tax return for instructions.