Help i have feelings for my cousin?

The other day we were playing at beating each other up, we were rubbing and getting close all night when she grabbed my penis and balls and wouldn't let go, i started to get and erection and she smiled at me and started un zipping, point is shes really hot and she was wearing an almost see through dress, she still didn;t let go but just took my penis out and started massaging it. she put my hand under her skit and i just started feeling and rubbing soon after we had sex and she orgasimed so loudly i thought the whole house would hear, now I am scared the family knows or that I have done a bad thing, I haven't seen her since and when she left she just smiled, we didn;t use protection and I am scared of what my parents will say if they found out, she is my first cousin, what should I do?