Blackmailed by my little sister because she wants me to play with her

I am a Sapphic Lesbian and only my sister, my brother, and his gf know and they are supportive. My parents are homophobic and today my sister told me "I'll tell dad your secret if you don't play with me", seen from any point of view, this is blackmail. I am honestly scared because I have no idea what he'll do if he finds out, now I am proud to be lesbian, but the fear of my own dad hating me or worse scares me. Now he'll probably use the bible as an excuse but me personally, I am not Christian. And that's a whole can of worms I'm not opening right now. But my sister only said "play with me tomorrow" so maybe it's not technically blackmail, but it still scares me, y'know? I'll update tomorrow.