Really anxious, need advice.

I turn 21 this month but still live with my parents as I’m still in college. I’m very dependent on my parents and love them very much. I have a boyfriend of a bit over a year, and I am sexually active. I’m on the pill (my mom knows this, but learned that I was keeping it a secret.). My parents are incredibly strict and my mom has asked me if I’m sexually active. I always panic and say no. I can’t keep doing this for multiple reasons. I need to tell her, but terrified is an understatement. I don’t want her to be disappointed in me or for our relationship to change. I know I shouldn’t have lied but in the moment I felt I needed to. What should I do/how should I do it? I know that this is all on me, but please be nice. 😭