apple watch face is coming off

This is most often a symptom of an older watch, with a swelling battery. Apple won't repair a watch in that condition. Power the watch off and don't use it. Schedule an appointment at your Apple Store Genius Bar for evaluation and options. Apple will usually offer an Out of Warranty replacement for a fee, but depending on the age of the watch, it often makes more sense to recycle the watch, not get a replacement watch for a fee and spend the money on a new watch.

Since you don't say which model watch you own, you can see the out of warranty costs in this link --> watch Repair - Official Apple Support