If I were you and you are happy with your present price, cabins and date and only unhappy with your TA, I would keep what you have. I my opinion you don't have a bad deal and I don't think the price will drop anymore if it does it probably be for new bookings only. On your next booking get a new TA, but for this one stick with what you have. Thats my advice is don't shot yourself in the foot. Relax and get rid of all this stress.