The nightmare before Christmas has a explanation mark next to it and is not letting me download another world

I went onto minecraft about 6 days ago and I wanted to make a nightmare before Christmas world and it would not let me. And it had a explanation mark in blue next to it I'm not quite sure if I have made too many worlds of it or I'd there's just a type of problem with the world. Can you please fix this bug and let me play the amazing game/world again. 

Thank you