Sounds like it should have flushed it pretty well.
I would have preferred to stick with the tried and true method of just draining the old stuff and refilling, sounds like after what the cooling system has been through that the old green stuff is long gone though.
The gallon you put in should be mostly mixed by now (assuming you drove the car to PepBoys).
If the ratio seems strong at this point (-40 or colder), I would leave it alone for now and recheck it in a week.
If it seems rather weak now, say +10 or warmer, drain or siphon off 1 or 2 quarts, add an equal amount of undiluted antifreeze, and recheck in a week.
Reinhard, since he had the thermostat removed when he ran water through it, it should have at least weakly flushed the engine block.