What am I to think about girls at my college if they are unkind to me but nice to each other and the lecturers?

They sound like a bunch of brats to me. The lecturer seems very unfair. You have to break out of your shy shell. Sometimes people are mean to shy people because they can get away with it and it makes their immature egos more powerful in their eyes. Shrug them off and don't let them matter to you.