How to tell if a girl likes you?

I go to school with this girl, we have had a few classes together, and she is part of my group of friends. Recently (last few weeks) we have started to talk alot more. At first it was a bit after class but now for even longer, she also added me on facebook and what not. She asked me if I wanted to stay and watch an event my school was putting on, so I stayed and we didn't even watch, we just talked the whole time. She looked very interested the whole time, asked questions, laughed alot, and sat pretty close, also never looked at her phone besides to show me something. She was also very open about herself. Then a few days ago after class we talked a bit, I knew she was done and going to head home, but she kinda looked disappointed, almost like she wanted me to ask her to do something.

Whenever we first see each other in class she always looks at me and smiles, and looks me right in the eyes, I make sure I smile back at her as well. I can tell its a genuine smile as well, not forced or anything. She also acts differently when we are in a group of friends together, almost as if she is nervous.

I am probably just over analyzing everything, but does it sound like there is something there? because I really like her as well. How could I tell if she is just being friendly and doesn't see me in that way? I am in University but It feels like I am still in jr high! I am so bad at this.