Affiliate Marketing Secrets

My senior year in High School (im currently a college freshman) I created a short film with another guy. This dude was failing the class *radio-TV* and the teacher told him in order to pass, he MUST make a video. So he approached me and asked me to work with him on something. He came up with a plot that STUNK. I decided against it, and I , i repeat, I wrote a new story and showed it to him asking would he wanna do that. His exact words were “I don’t care”. Long story short–I just wrote a screenplay based on it and copyrighted it. I’m fearful he may try to sue me claiming it as ‘his’ when he BARELY did anything with the youtube version. I did all the work. I just gave him all the credit so he could get a good grade, but he never wrote anything. At least not the final product which was ALL my ideas. There is nothing in writing saying he wrote the story. It’s basically just word of mouth. There’s not even a script based on it, it was all improv when we filmed it. So he has no solid information saying he created it, because all he really did was reap the benefits off of my hard work.
I’m also afraid because he’s a very violent gang-affiliated guy. It’s not worth getting killed over. So who’s the rightful creator? Me or him?