Hey,
SelfControl requires you to type in your password to start the blocking. Your script does not reference the user's password at all. I suspect that might be the problem.
There was an additional forums post about SelfControl from February 15 that you can find here: http://www.alfredforum.com/topic/5496-distraction-free-freedomapp-workflow/?hl=selfcontrol. His script does reference entering your password.
Hope this helps