What's wrong with me?

[dncr20]

Okay so to be honest I don't think I'm that pretty. I'd say I'm probably average or slightly below. Snce this school year started I've had multiple guys tell me I'm pretty through twitter DM or on Instagram. They also say we should start talking because is seen "nice" or "cool". I don't mind meeting new people, I actually kind of enjoy it. But whenever a guy says that they completely ignore me at school or afterwards. I see them stare but they don't come talk to me. Why is that? I'm quite in classes that my friends aren't in, but in other classes I'm outgoing. Am I intimidating or something...? How can I change that? I want to start talking to new people...