What does this mean confused?

well when I'm in class some times I will look around and I will notice a girl looking me stright in the eyes this happens to me quite abit with lots of girls like the time I was fixing my sock in class and I got a feeling some one was looking at me and I look up and there is this really pretty girl with blue eyes just looking at me and that made me super nervious so I just looked away asap I don't think I'm hot so idk why this happens and most of the girls that look me in the eyes are really hot and I'm just really confused they never talk to me but yet I'm really quite and don't say much