I feel embarrassed about being a virgin. Why?

I'm 20 year old female and my friends always talking about them and guys and they always ask me and I'm like "Uh, I'm a virgin" I feel good about it till people ask and I don't want to tell them. My sisters are virgins (21, & 16) we're not a religious family or anything like that we're just virgins by choice and we're all cool about it, I'm cool with it around them because we all know each other. But I either get those people that say "No, you aren't" and that makes me mad because it's like you don't know me to tell me no I'm not. But my friends always want to know more they'll ask if I ever did anything with a guy and I've done ZERO things, NADA, NOTHING at all so it make me feel awkward and ashamed kind of and it's like I'm the bad one but it's like I feel almost embarrassed to say it. Like I recently just seen a male private part because we were flashed up until some months ago I never had. I don't want to lie what should I say? Cause they always want to know why and it's like cause that's just what I want to be. I don't want them to think I'm a prude or think I'm better than them cause I don't think that.