What does it mean when a girl catches you looking at her and she smiles back at you when she catches you? Does she like me? ADVICE?

She some times holds the gaze or looks back towards the front. This is in college. I've caught her looking at me when we r waiting to be given instructions or waiting to be sorted into groups for a project. Not so much on giving instructions but when we r crowded around the teacher or table I've caught her a couple of time. She doesn't do it when the teachers talking. Weve never talked to each other. She sits at a different table and I sit behind her. She sits by her friend. does she like me. Today she seemed sad. I still haven't had the nerve to talk to her. She didn't do anything today so. She didn't do it to me today but she seemed sad about something all class. I dont see her again til Tuesday.
What does it mean when a girl catches you looking at her and she smiles back at you when she catches you? Does she like me? ADVICE?
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