Twilight. Nice. My older brother adores that series at the moment (I haven't read it yet!).

Anyway, dreams can be weird in a variety of ways. Either a situation is out of place, someone's actions are out of place, or you are experiencing a deep emotion. In your case, I'd say it's the situation. Is your school really putting on a play about Twilight? I used to be in the school plays and musicals, so I'd often have dreams about play (being late, getting assigned a different part, putting on a new play, having an unplanned rehearsal or show date, not being in costume, etc. Funny, I never dream about forgetting my lines!).