Back came off my watch

Time to set up an appointment to have it looked at. I would suggest going to an Apple Store.

Make a Genius Bar appointment to have your Apple Watch checked:

http://www.apple.com/retail/geniusbar/

Hope this helps

Hi

Apple Watch is not user-serviceable.

If the issue is not covered under warranty or any other Apple policy - if you have a 1st generation model, then be sure to ask, with specific reference to potential battery swelling issues - then your Apple Watch may instead be eligible for replacement via chargeable, out-of-warranty service or via AppleCare+, if previously purchased.

Out-of-warranty service prices (and AppleCare+ service fees / excesses) vary by country and by Apple Watch model. Pricing for the US, for example, is detailed here:

Apple Watch Service Pricing - Apple Support

Contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider to arrange for your Apple Watch to be inspected and to establish your available service options:

• US: Apple Watch Service Answer Center - Apple Support
• Elsewhere: Apple - Support

I'm afraid that no-one here can tell you what Apple will decide in your specific case. You are not talking to Apple here - this is a user-based technical support community.

In the meantime, note that Apple advises that you should not continue using a damaged Apple Watch.