My suggestion is to chop it back. Bouganvillas do not like to be fussed with, and they have a very delicate root system, they dont do well transplanted. They like to be left alone with minimal watering. We wanted to get rid of our Bouganvillas because they create such a mess with their papery blooms that fly everywhere so we cut them all the way back to the ground. Wouldnt you know it, its coming up more beautifully than it ever has. Its like, "Ah dang it, we gotta kill this thing AGAIN?" So my suggestion is to cut it way back and you will get new, tender shoots that will bloom beautifully for you.