Revealing mistake: After Kenan gets his head stuck in the bars it becomes obvious on multiple occasions while Kenan is moving around that the "bar" on his right is fairly flexible, presumably made out of rubber for the benefit of the actor.
The Raffle - S3-E3
Revealing mistake: Kel does not drop anything in the tombola. (00:13:20)
The Raffle - S3-E3
Revealing mistake: The woman who wins the TV supposedly hits Kenan with it, but very obviously misses. (00:17:05)
The Raffle - S3-E3
Revealing mistake: When Kel is trying to stop the woman taking the TV, he grabs her leg. If you look closely, he hasn't got hold of it at all. (00:17:10)
Answer: Kel.