Restart your watch by pressing the side button for a few seconds, swiping to the right on the "power off" slider, waiting for it to shut down, then pressing the side button for a few seconds again until you see the Apple logo to turn it back on.
If that does not work, then try un-pairing your watch with your iPhone and the re-pairing it:
Unpair your Apple Watch and iPhone - Apple Support
Set up your Apple Watch - Apple Support
A backup is made automatically as part of the un-pairing process.
If that still does not resolve the problem, then you may have a hardware issue, as there is no function that would "lock" the Digital Crown. You can take it in for service or arrange to send it in at http://getsupport.apple.com.