Realistically, if you followed instructions and used appropriate backing and screw pattern for the ceiling cement board, you're probably fine. But if you affixed the cement board to your 24" on center trusses or 16" on center floor joists, the cement board doesn't have enough support. Probably needs 12" on center and blocking at any seams.

Also, did you install the cement board over drywall? Or directly to wood framing?