Step sister pregnant and now so am I

Hello, wondering what I should do. She’s due in March and I’m due in June but no one knows yet (minus my mum) we are planning to wait until we know the gender but I’m wondering if I should tell my step sister first? I don’t want her to think I’m trying to steal her attention (like because all focus is on her right now and her pregnancy)

My pregnancy wasn’t planned and also there’s this thing with the family where no ones had any girl baby’s and she’s just found out she’s having another boy, just don’t want to step on any toes especially if I end up having a girl but no idea yet!

We were planning on surprising everyone