Did you make a payment with the extension? The extension gives you more time to file the return. The tax due was still due April 18. Your return is probably assuming you made the payment.
So be sure an extension payment doesn't automatically show up on your return! Check 1040 line 31 which comes from schedule 3 line 10. You may need to delete it. See this Extension FAQ for how to get there. Then you can change to amount to zero.
https://ttlc.intuit.com/community/tax-payments/help/how-do-i-get-credit-for-tax-payments-i-made-with...
