If your Apple Watch does not respond to touchscreen inputs as expected, then the following steps may help:
Remove any screen protector, case or bumper that you may have fitted to your Apple Watch.
Clean and dry your Apple Watch, being sure to follow Apple's cleaning instructions:
Restart your Apple Watch, including force restarting it if it cannot be restarted via the normal procedure:
If the issue persists, then I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance: