After removing the spa light in our gunnite pool for some maintenance I've noticed that the light housing is set into a bulging area of the wall. It looks as though this is the way it was constructed, so it's not anything I'm concerned about.

However, the inset housing does not sit flush and leaves a gap between the wall and the flared edge of the fixture. Does anyone have any idea if there is any type of gasket or product I can use to close the gap and make it appear flush? It looks kind of tacky the way it is right now.

Thanks in advance for your help