I just got through the game once, and I intend to see what happens when you make the wrong choices for fun later, so I dont know what scene you are missing exactly but red just means you are missing a scene (not always H-Scene, cant remember if this one is) because you don't have enough "points" with the girl the scene is for, you havent picked enough of the choices that would make her close enough. Youll have to go back and fix that.