Blooms on plant but not openning?
Can you put an image here so I can see what's going on? My guess would be low humidity. You can try spraying the plant once or twice per day. This can help.
Here is an article for more information on the care of these: https://www.gardeningknowhow.com/ornamental/cacti-succulents/christmas-cactus/advice-for-christmas-cactus-care.htm