Help me calm down my girlfriend

Hey there, I'm gonna keep this nice and short. Me and my GF have been dating for about a month and a half, and we've known each other for 5 years before that. We're trying to keep our relationship between close friends only, and never interact in school since our school is really small and word gets around easily. I messed up two days ago by letting my teacher whom i'm really close with, tell my classmate about me and my GF. I never thought about how serious it could be (nothing has been exposed yet), and didn't even think about asking my GF beforehand. I know i'm an asshole for that and i understand how serious it is to not ask her first, but i made a mistake and im really sorry about it. She's really mad right now, and i was afraid of her saying something she didn't mean since she clearly wasn't thinking straight so i told her "Let's text later so idon't say any wrong things" when she replied with "you mean 'so you don't reply with any MORE wrong things, but okay" then i asked her if 7 PM was a good time then she said she doesn't care. I'm really confused right now and i'm scared of losing her, especially after we've been friends for ages before things got serious with us. Please help me, she isn't like any other girl