What should I do about punching my dog once? I feel bad about it.
Why did you punch your dog?
Because he's a stupid animal with a shitty attitude.
Most animals are defenseless, and hitting one could hurt it, break bones, or cause internal bleeding. If it has a bad attitude, you might look into how you train it. Most dogs will behave how their owners make them, and if it has a bad attitude, it's your fault for poorly training it.
I'm not changing how I work with my dog and he doesn't need to obey.
Abusing your animals is wrong. If you do this, it shows that you are not able to properly handle training or owning a pet. You should be sure watch training videos on YouTube that will demonstrate proper ways to care for and train dogs.