I have a thing for this girl in one of my classes, so a couple of weeks ago I introduced myself and we chatted for a bit, I thought we hit it off pretty well. Then a guy that she already knew came over and she left for lunch with him, so I didn't ask for her number.

Last week she started a conversation with me at the end of class, then ask me for my number because she wanted to hang out. She texted me a day later to give me her number.
Then the next day to ask me where I was on campus, but she only came said hello and that she would see me in class.
in class she was very friendly with me and invited me to come smoke weed with her after class... So we did that then chilled in the library doing homework and listening to music.
Later on in the evening she text me "hi 😊" then I replyed "hey what's up? 😉"
Then.... Nothing she took hours to reply.. She just went cold for no reason. I've ask her to hang out a couple of times and she's given me excuses and takes hours to reply..

What should I do? should I ask her about it? If so should I call her or wait to see her at school again? What would be the best thing to say?
I'm just kinda stressed about it, a girl I find very attractive mentally comes along and gets me interested and then goes cold..