Apple Watch: how to close app

[NorthOfYYZ]

Plan

Premium

Country

Canada

Device

Apple Watch 5

Operating System

WatchOS 6.1.1

My Question or Issue

I’m stuck - if I start the Spotify app on my watch, it takes over and I can’t seem to close it. I go to the Dock, swipe left & tap on the X, but as soon as I’m back to the watch face, Spotify is there - when the watch is not active, the face is replaced by the digital clock and if I tap on it the Spotify app pops up. 

Any help is appreciated.