Please grow up - I don't want a baby!

Well, disregard my previous post where I was glowing with the wonderful success we had the other day. Not only did Harrison go pee in the potty that afternoon but he also did it for Dave when he got home from work. We were silently high-fiving each other. BUT... since then he refuses to do it. He won't try. He screams and cries. When asked if he needs to go he says no and then pees in his pull-up. I'm not happy. It's really ridiculous, honestly. He is old enough. He more than gets it. He just doesn't want to grow up for some reason and it's driving me crazy! He loves to be a baby. Look, if I wanted another baby I would just have one. I don't want one - I want my 3 year old to grow up!