You will need to file using the W2G forms. The IRS received those forms as well so they are looking to reconcile with that information.
You enter the form W2G in the "Gambling Winnings" topic in the "Less Common Income" section.
After entering the W2G form information you will be given the opportunity to enter your gambling losses up to the amount of your winnings. Those losses will automatically transfer to your Schedule A as itemized deductions should you itemize.