Apart from this, please let me know if your sketch on your M0 works as described in your post, because on this M0, some parts REALLY DO NOTHING, as per my previous stencilled Word doc.
The code that I supplied to output 370Hz PWM on D7 works. I've tested it on my Zero, my multimeter reads 370Hz.
All I can suggest is waiting until you get your Genuino Zero and the Arduino.cc IDE up and running. At least then we'll be singing from the same hymn sheet.