My experience in the past is that as long as your exact same itinerary is still available, give them a call and they will give you a JetBlue credit for the difference. No refunds that I have heard of.....just a credit that can be used within 12 months.
We've done this for two previous vacations and right now I have a $275 credit that will come in handy for next April's vacation!
HTH's!
Sammy