I met a girl in one of my classes and we became lab partners. The first 2 days of class we barely talked (class is only once a week) but the third class we actually had an experiment to do and I feel like we really hit it off. Like we were making jokes and laughing 90% of the time and I made a bet with her about our professor's tattoo and the loser would have to buy coffee. Long story short I won the bet and then I bet her that there wasn't a Starbucks on campus and this bet was for pizza. When we got there she won the bet so I owe her pizza. My only concern is that I saw a glimpse of her phone and noticed a dude was her background so I made a joke that asked about her phone background because I thought she had a boyfriend. She changed the subject and we kept talking about other stuff. I haven't texted her since we talked cuz I was busy so I was thinking about texting her today to pick a pizza place. How can I escalate and show that I like her when we go out for pizza?