I have to say that at 12 weeks old, you're not going to find anything more demanding than that. I know my puppy was non-stop at that age. I know why you feel this way. I'm not trying to talk you out of returning the puppy, but I did talk a friend out of returning hers. I told her that if she stuck it out, she'd be happier in the long run. With her, I wanted her to keep the dog because of security reasons - a single woman living alone. She's thanked me a million times for doing this - once her puppy grew up to be the wonderful companion he is today.
Introducing structure and down time to a puppy's daily routine is what it takes. Exercising them so that this down time is quality sleep time is how to make it work. Letting them know that the down time is non-negotiable is necessary. So put a nice bed beside you, with a tired puppy on it, and teach 'relax' and ignore the puppy until it falls asleep. I think you might be being too hard on yourself. Puppies might want constant entertainment, but that's not realistic.