You're right, it was 1040-X
The problem is that after making the amendment, the value shown on Line 6-Column B (Tax Liability-Net Change) was echoed on Line 22 (OverPaid) and Line 23 (Amount to be Refunded). In my case it was shown as a $418 Refund. When I manually calculated it, I owed $3,744.
Another strange thing is that my Payment Voucher shows the correct Amount, which I will be paying
