I obviously wasn't clear enough so I'll be bad mannered and shout
BUY A NEW TICKET
The USA, like most other countries, says it wants you to prove you are going to leave their shores after your visit and the ticket copy (not your itinerary, it's not the same) is the way you do that. I've been asked for it within the last 5 years and I know of 2 people who were deported for failing to produce that ticket copy (at least that was the story told to their employer).