Put your AudioStreamPlayer at the root of its scene:

This is all that should be in the scene. No Control above it.
Then, make sure you're calling it the Autoload way and also that you are using the correct variables and function names.
func _pressed() -> void:
if ControlMusic.playing: #no $, check "playing" not "play"
ControlMusic.stop()
else:
ControlMusic.play()