I'm really frustrated

I'm really frustrated So, I always go to this market to buy stuff. There is this gurl at cashier I really like. When we talk about daily stuff I will speak fine with minor stutter. However, when I want to ask her number or ask her out I get really nervous and I can feel that I will stutter really badly so I stop. I was able to get her Instagram thou; but I don't want to ask her out on social media, I feel like I will come like unconfident. It's really frustrating that I can't tell my feeling face to face. I just wish this thing go away.