Why can't I delete scenes?

I made a short story about two cats and they are the only two characters in the storyline. In the middle of the video, pops up a little boy in the yard of the cats and the next scene has a different boy with a dog. Why is the app adding characters of it's own? I used almost 5000 credits and the story is ruined. Am I supposed to redo the story and use more credits for the app mistakes?