I don't know what to do..

I'm 9 weeks pregnant and I have no told my parents yet, all of my boyfriends family knows and they are so supportive. They keep pushing me to tell my parents, the only reason I keep pushing it off is because I'm really scared of my dad and what he'll do, I don't think he'll hurt me but just the thought of him being mad scares me. I'm ready to move in with my boyfriend because I think it's best for the baby, but I have a feeling if I tell them in person my dad will do anything possible so I won't leave. My boyfriend told me to just pack my things and leave while everyone is asleep and just leave them a letter on why I left. I need advise, would leaving a letter be the best option? I'm really nervous and don't know what to do. I just need help.. Thank you.