How do I avoid getting wedged between an outer water layer and the edge of the map?

In Map maker I like to involve vast areas of water surrounding my showdown map but when I play Darrel and role out into the open areas of water I seem to get wedged between the water and the edge of the map, is there a way to avoid this? I can not place a wall on the outside because it involves a one block gap, How could I fix this water problem??