So university just recently started

So the other day after getting out of a class , I saw a couple people i knew a bit from high school. One being , a guy that had class in a couple minutes. the other being this hot girl in knew a bit from high school ( just from her coming over to my place for gatherings and through some friends )

So , she asked me what my schedule was like right now . I told her i had an an hour and a half wait until the next class. she was like oh really , i also have some time right now . wanna chill ??
I automatically started to think to myself*wow ..wasn't expecting that * so i go with her and follow her to the very back of the library . im thinking damn im going to have to keep the conversation going for an hour?!.
So i keep the conversation going , not saying it was the most fun convo ever but i kept it going no awkward pauses or anything.
next thing we know some other girl who we both dont know jumped into the convo.

the new girl kinda pissed me off because it kinda ruined my game because the new girl and the girl i was gaming got into a good convo. and she wasn't really my type and i could tell she wasn't really feeling me.so i tried to keep up in the convo but it was hard. next thing you know it was time to go to class so i left

so just yesterday i saw the girl who asked me to chill passing by on campus. she was with some asian guy and we both saw each other but nothing was said and she seemed to give me a bit of a disappointed look..

what should i do the next time i see her?

what really pisses me off was that i was about to find a way to get her number and then the other girl jumped in.. so really i took nothing out of it .