You just fragged it into two!
Super glue is hard to use on soft corals - they slime up and the super glue comes off.
What you could do is use a needle and thread and "thread" it with fishing line onto a rock. Once it bonds to the rock, you can just cut the line free. Or put both halves into a plastic bowl (like a cream cheese dish or something) with a mesh net covering, so it doesn't blow around. In the bowl has rock rubble, and it'll settle on a piece and bond.
Or just use another rubber band and take it off earlier!