Hmm yeah perhaps you did come across a bit clingy to her? Who knows, she's the one sending friend requests and smiling. I wouldn't bother messaging her again, there's one thing if she's not that interested, but she sounds like she was being plain rude. Maybe she just wanted the attention but doesn't want to actually get involved with anything, or maybe your personality wasn't what she's into. If you see her again just smile and keep on walking, if you bump into her on a night out could briefly go over for a friendly chat. But I wouldn't bother wasting your time. If a pretty girl is smiling at you and adding you on facebook, you're probably quite attractive