This girl always leaves early and with a brisk pace, so I couldn't talk to her then, and the lecture theatre is very quiet during the lecture. The only thing I can think of is passing notes and whispering, she also sits at the back of this relatively small lecture theatre (50 seats) in like a cut in the wall only big enough for 3 regular chairs without desks. She sits on one with her bag on the other 1 with one chair left empty. I feel if I sat on the other it would be extremely obvious and desperate and creep. Even then whispering and passing notes seems also a bit desperate and creepy. Any advice? We've been having eye contact but she's impossible to read. I realised she worked at the local subway but she didn't say anything and I didn't realise it was her until afterwards. Will it seem desperate if I talk to her there?

Please help.

Edit: We have made eye contact multiple times in lectures. For as long as 3-4 seconds. On one occasion we had eye contact for 5 seconds, I looked away, then looked back she was still looking at me and we had looked into each other's eyes for another five seconds. Then I looked away. Then she left early. I should add she doesn't always leave early the above was wrong. But in this instance she left directly after. I should also add I can't read her. At all. She would be a brilliant poker player, as when we stare into each other's eyes she moves not one muscle fibre of her face. Thank-you everyone for the sound advice so far, but I would be very interested to see what people have to say about this and how it changes the situation.

*Edit: Now that I think about it , I have a pretty blank face and she could be in the exact same position lol.