Edit: That was just her fantasy right? if so then its not bad
Yeah, just something Yuuna was imagining.
Which is a nice moment of irony since she was telling her girlfriend earlier that there’s no reason to get scared of anything fictitious or imagined since it’s not real, yet when she imagines herself and her girlfriend in the position of the characters in the movie, she becomes terrified at even the prospect of losing her girl in such a way and realizes that fiction can indeed induce real terror.