looks like its rotting n diatom algea growing on it. try increasing water flow. a dip in Revive or similar may help.
i I used krazy glue because I had a number of people tell me its safe...
It's fine, you just severed it from the parent colony and you're worried about choking it lol. Seriously, though it's fine. if you are worried you can lodge a small rock or something under the band to relieve some of the pressure on the actual coral.