Everyone has bad days. It's not the end of the world. You learned a lesson this week and you'll probably improve on it next week.
When training a puppy, find out what motivates the puppy. If he doesn't like cheerios, then he's not going to want to work for them. Boil some chicken breast and cut it up into little pieces. Cook some london broil or some other lean steak and cut that into little pieces. Bring his favorite tug toy that he only gets during training. Get something that will get and keep his attention. Dry, boring cheerios just isn't it.
And why can't you play fetch with a dog that's teething? Who told you that? If the pup likes to fetch, by all means, let him fetch.