When I've guessed wrong, I've also been rewarded with unexpected large dollar figure checks in the mail. I did once make an error that cost me, and someone at the IRS was excellent in working together over the phone to get things square.
But did they also send any interest? Notice if you owe them, you also owe interest, unless you negotiate. If they owe you, you don't usually get the interest sent do you.
"I can take out $2k to fix the flooded basement and it'll cost me $200 in penalties? OK."
Source: I've filed a 1040X twice, both times in my favor (due to my own mistake I noticed on my own later). The IRS issued me a 1099-INT the next year for the interest they paid me. The rate was substantially above market!