Girls, Why does she sometimes act this way?

So at university me and a girl followed each other on social media. I didn’t know her in person yet but thought she was cute. I had a party coming up so I invited her as it appeared she did not have a boyfriend. Unfortunately she said she couldn’t come because she was visiting home on that week
I didn’t message her again or ask her again. But now at the gym she notice me and who I was. She keeps staring at me all of the time. I am very built because I have been training a long time an a competing athlete. I notice her front also keeps looking. But when ever I finish an exercise she will watch me and look kinda nervous and quickly look away. I’m normally very focussed. But she keeps doing it. I train very hard and just keep to myself so don’t do anything out then ordinary I am there to work. But then I can see her from a distance watching me. Then if I look back she acts nervous and quickly looks away and so does her friend.

Also everytime I look at one of her recent posts on social media , she looks at mine. I just don’t get why she look so nervous and look away quickly. Or keeps watching/starting at me. I did ask her to a party and think she cute but I don’t do anything obnoxious I just keep to myself and train hard
Girls, Why does she sometimes act this way?
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