The Villainess's Sweetheart: The Movie Emperor's One True Love

Su Xiaonan comes equipped with a Tsundere System and transmigrates into an otome game as the villainous supporting character, who also happens to be engaged to the game's ultimate villain and final boss. She plans to follow the plot obediently, but who could have guessed that the villain wouldn't stick to the script and would kiss her with a perfectly straight face? Hey, hey, hey? Did I get the wrong script? I'm the villainess, so how did I become the heroine?