There is a simple way you can quit apps that are not functioning correctly on your Apple Watch.  To quit the application, first load the application that is causing your the problem, then press and hold the power button, this is located under the digital crown.

Once you are faced with the menu to power off the watch, press and hold the button once more and then it will close the problem application and you will be back facing the main screen with all your applications. 

I showed this to someone today, as they were switching off their watch each time an application was playing up.