Oh boy! I made the same mistake and now mine occupies about 3-4 times the area in the pic on the right herethe pic on the right here (that was taken last Oct). It's hard to tell if you're really done pulling it out, because the stolons could have propagated quite far.
I don't know of an easy way (I doubt there's one...). The approach I'm taking now is to mercilessly cull most of it (leaving only what I need). Later, when it pops up in a new area, I dig around and cull that. That way, I don't break my back trying to dig in places where I can't be sure if it's there or not. Besides, as Kate mentioned, it's not really a bad thing — I don't mind its smell, and it certainly has uses. So I'm not desperate to get rid of it in one sitting.
