Getting aroused seeing my sister fucking dad

Dear Diary, I have always been a very shy girl and my older sister Emma was the outgoing cheerleader in the family. Every now and then I'd catch glances between her and our brother but I was too naive to see the truth until one day when I caught them fucking in a classroom. Emma swore me to secrecy so Daddy wouldn't find out and told me we'd talk later. When I went to her room I heard moaning and peaked through the door. Imagine my surprise when I saw Emma was fucking Daddy. I was shocked and aroused at the same time but instead of leaving I kept peeping through the door. I started touching myself through my dress and imagining it was me Daddy was fucking. The thought of him enjoying my body was so intense I came right there in the hallway. I think theres something wrong with me.