I know the Abbey in this novel is not supposed to be scary, but it is still a new experience for Catherine -- being in the Abbey with the Tilney family. Of course the novels had influence, but it could also be that Catherine is nervous in this unfamiliar situation; and the General, although apparently nice to Catherine, can be frightening at times. Catherine saw enough in his severe treatment of his daughter to dislike him, and the novels she read made her imagination run wild.