This is usually a result of the ratio of liquid to bread being off. As long as you use only 1 can of coconut milk and a full 12 pack of Hawaiian rolls, you should not have watery bread and butter pudding. It could also be because the bake hasn’t cooked long enough for the eggs to set. If you believe this to be the case, just continue to bake until the pudding only gives a slight jiggle when shaken gently.