Why did pony and johnny end up sitting next to marcia cherry?

You're likely referring to the characters Ponyboy Curtis and Johnny Cade from the novel *The Outsiders* by S.E. Hinton.

However, there's no mention of a character named "Marcia Cherry" in the book. Therefore, Ponyboy and Johnny would not have ended up sitting next to her.

It's possible you might be thinking of a different character, or perhaps a scene from a movie adaptation of the book. Can you please provide more context or details about where you encountered this information?