Did you rec've a 1099misc form?
Basically nothing is going to happen. Over the summer, or early next fall, you're going to receive a letter from the IRS showing the amount you "forgot" to include, the estimated tax, and a due date to avoid additional penalties.
The penalty that will be on the letter, not including if it's not paid by the due date, should be minimal, probably between 100 and 200 dollars. This of course is assuming they filed these winnings, which they probably didn't if you never received a 1099misc.
And don't ask me how I know all of this