Mom announced my pregnancy

So I found out I'm expecting. I was maybe 4 weeks and decided to tell my parents, best friend and my partners parents ONLY until my 12 weeks scan. I made that choice in case of miscarriage AND because I wanted to show my ultrasound and make a special announcement which my mom HELPED ME WITH. Saying I should make it cute and special.

Well my best friend was at my family Christmas party and told me my family kept coming up to her asking her if I'm pregnant.

The ONLY person that could have told is my mom. My best friend has NEVER EVER let me down or told my secrets. She'll lie straight to anyone's face for me. My dad doesn't talk to my moms side of the family after their divorce and also keeps my secrets. He actually was 100% behind me on not announcing until my first scan. He said "I really agree with that, anything can happen". He didn't even tell my sisters, who found out. I was the most excited to tell them myself. How do I confront my mom without losing my shit on her? 😧

PS: this is my FIRST pregnancy so I'm extra upset about it. Even my MIL asked me if she could tell my BIL but my own mom didn't.