Though not to Jamaica, I traveled with my wedding gown as well and carried it on in a dress bag. I was travelling with Air Canada and the cabin crew hung it in the First Class closet. I would not recommend checking your wedding gown - in fact I would do everything I could not to check it. I was once given the advice to never check anything that you couldn't replace. Lost luggage happens and what a nightmare if that was you gown.

If they won't let you carry it on, I would ask if they would let you check it at the gate and pick it up when you are deplaning, like they do with baby strollers. That would minimize the chances of something going wrong.

Our journey took us through three different airports and all along the way, when I told people it was my wedding dress they took extra care with it, going through all the scanners, etc. I doubt you will have any problems.