Help about this girl?

so i've known this girl for about 3 years and i really like her. We only have one cl together at school but we talk and text a lot. We don't hang out that much because were always busy but golf season is starting up and we both play so we will hang out a lot there. She flirts with me a lot and I think she might like me but I'm not sure. We went to a school volleyball game yesterday and I was planning on asking her out then, but she started acting really weird. I wasn't like trying to make a move on her or anything, she was just acting strange. She was like secretely talking to her friend a lot and I overheard her friend say "just sit on his lap" (because I took her seat) and she responded with "ewww no". What does this mean? She was acting really different and I don't understand why. Why was she acting like this?