To temporarily stop StretchClock from launching stretches: 

1) click the "pause button"

You can unpause StretchClock at anytime.


To remove Stretchclock  from the desktop sidebar
(if you want to run it again later):  

1) click the "x" on the upper right side of the clock gadget 
remove StretchClock

OR you can Completely remove it from your computer by using the gadget gallery.

1) Right click on the StretchClock gadget in the windows sidebar

2) Select "Add"

3) You should see the Gadget Gallery:

Remove StretchClock

4) From the gadget gallery, right click on the StretchClock icon
5) Choose "uninstall"

Following the steps above will stop all Stretch Breaks and will remove all of the files that were installed.