Girl invites me to the movies

Girl from bumble adds me on ig and adds me to a group chat where she’s telling her friends that I’m cute and that the other guy in the group chat (giving him a fake name Mark) needs to not be jealous.

She seems interested and invites me to a movie. I say sure, we organize it and plan a time/location. But then she says that Mark is joining us at the movies

I don’t really know who Mark is but I think this is giving me red flag vibes. Does anyone know what might be happening here? Should I still go, or what should my next step be? I’ve never had someone invite their friend to a date, or whatever this is