Tim--It sounds like your flight has just become sold out, after you booked, which should be none of your concern. Make sure you check in as required three hours before your flight and you should be fine. Do you have a seat assignment? If so, I think you're fine. If you DON'T have a seat assignment, get one. I don't think that Jet Blue has any types of seats that you have to pay extra for a seat assignment, unlike AA and Delta..