You didn't embarrass yourself, you showed confidence by going up to those girls and talking to them. If you wanna get a girlfriend then, you gotta get tougher skin. If you really like a girl, just tell her that. If she laughs in your face and doesn't reciprocate that energy than move on. This isn't a stuttering problem, this is a self esteem issue. You need to have faith in your voice no matter what happens. If you have something important to say, just say it.