I've paid penalties for an IRS mistake. I submitted my returns, and the IRS said "We found a mistake, here's $300 more than what you thought we were going to re

I've paid penalties for an IRS mistake. I submitted my returns, and the IRS said "We found a mistake, here's $300 more than what you thought we were going to refund you!". A few months later I got another message from the IRS. "You made a mistake and got $300 too much! Pay us back + interest." Didn't feel like fighting it because I heard that can go south easily, especially for such a tiny amount, so I paid it back with the interest.