The "Stan Wrong Song" is an apology song written by Mabel Pines and it was sung by Grunkle Stan after losing his and Mabel's bet to see who can make more money. It took at least 30 takes before Mabel (or Waddles) was satisfied. Stan seems to have liked it, since he sings part of it while shaving in Mabel's Guide to Fashion.
I'm Stan and I was wrong
I'm singing the Stan Wrong Song
I shouldn't have taken the chance
Now here's my remorseful dance