FADE TO BLACK
I like this! I think you can make the metaphor a bit clearer for what chess means. Does it mean taking risks to get closer with someone? Is the moral of the story that you just have to play with the right person? Is the chess game between Jane and Charlie a challenge to Charlie's strategization of trying to get a girl? Or his decision to attempt playing at all? It seems at the end Charlie becomes opened up to the possibility that he doesn't have to be nervous and people will want to play with him. Is the story Charlie triumphing over his lack of self confidence, or his understanding that sometimes he'll lose a game no matter what?
Continuing this thought to the title - En Passant is a tricky move. One that seems illegal, but isn't, and catches people off guard at the first moves of their pawn and captures them. Is there any symbolic connection to these ideas with the en passant? Is Jane the one who employs en passant? Or Charlie?
I think making what the challenge is clearer will help viewers be able to align with the stuggle and story for Charlie and root for him - unless it is that we aren't supposed to be, and have a critical outlook on his approach to relationships. The way you set up the character in the beginning - he seems nervous, anxious to make friends, not self confident, and overwhelmed. This makes us want him to succeed, seeing him struggle. But he doesn't seem to want a relationship until Thompson brings it up. We haven't even met Jane yet when Charlie begins his journey to getting her. Perhaps by introducing her at the scene in the coffee shop, maybe ignoring Sadie to look at her, or somehow he goes to the coffee shop just to see Jane, will provide a similar extension of alignment.
By maybe also refining the chess analogy for example will clear up for the audience where they are in alignment to Charlie's story and wants.
But overall I think you've got a great start, and would love to see you experiment a little more with how you tell this story! You don't have to of course, I think my filmmaking style personally is a bit whacky, but this is your short film, have the courage to think of the ways you find personally will powerfully communicate these essences!