I wholeheartedly agree with snoozeman on this one; you never want to pay in full before the final payment due date. Cruise lines hate to refund any money!
However, even though you have made final payment, the final payment due date has not yet arrived, so you should be okay. If they're not willing to refund the money, as was stated earlier, you can always cancel, get a full refund, and then rebook your cruise (but this time use an agent).
Word of advice since we're on the subject (this may not apply in this specific case, but thought I'd point it out anyway); if a special is offered 'for new bookings only' and the cruise line will not re-price your cruise, so you decide to cancel a current reservation then rebook it just to get the special, take notice that in the fine print this is not allowed. The cruise lines run a software package to catch people who do this and the discount rate will be disallowed and then automatically be changed back to the original amount. (There are tricks of the trade to avoid getting caught.) This type of practice use to be more prevalent years ago, but we haven't seen alot of it lately, so it's not as much of a problem as it use to be.