I think the "Cancelled" thing needs an explanation.
Did she come to her senses and get a drum kit instead?
"If you're good, you'll get a guitar. If you're bad, you'll get an accordion."
"We've gone over your records and we've found a typo. It turns out that you turned 18 last year. I guess you missed it. Sorry."
"I've already booked you to play at a rodeo."
"You can either have the guitar or that tongue tattoo."
"Mom! I didn't say that I, like, wanted a guitar, like for my 18th birthday! I, like, totally said that I wanted a guitarist! Duh!"
Let me know if I'm getting close.