According to JetBlue's 24-hour cancellation policy, customers have the right to cancel their flight reservations within 24 hours of making them and receive a full refund as long as the departure date is at least 7 days away. There would be no JetBlue cancellation fee. Additionally -

The vacation packages would not be subject to JetBlue's 24-hour cancellation policy.
cancellation fees for JetBlue within 24 hours - Whether or not revised reservations are made within 24 hours of the purchase, they are not eligible for a refund and can be cancelled. subject to a per-person cancellation fee based on the fare booked.
Returns at JetBlue When a JetBlue flight is cancelled with less than 24 hours' notice, the refund will be applied to the original mode of payment within 7–10 business days.
If a flight has more than 9 passengers, JetBlue cancellation policy would not apply, and the group cancellation policy would apply instead.
You can cancel a JetBlue flight within 24 hours by visiting the Manage Booking area of the airline's website or calling the JetBlue cancel flight phone number.