Did I do this right? I am thinking there should be no gap here at the bottom of the 120/240 dryer outlet?

That's fine if its secure to the wall. I see no stripped wires showing and it seems tight. The gap is normal. Some of the boxes have different configureations and that's probably what your thinking. Make sure your above the floor for water getting the floor wet if a problem arises. Make sur the clamp is tight.