I am in love with this girl at my grad school & she turned me down, but we are friends. can I change her mind?

she didn't really give a reason, but I am 90% sure she is single and I have never liked a girl this much - she is perfect for me. I have been super nice to her, even after being rejected. I helped her out with some stuff and did something nice around the holidays. We didn't know each other that well at first, but we went out three times just us, but they weren't dates, at least not from her standpoint. She recently asked to meet with me to get help with something, and while worried she might be taking advantage, I said sure no problem and met her for a few hours to help. She has opened up to me a tad more, and seems appreciative, but it's frustrating because every time I hang out with her my feelings really shoot up again. Perhaps I should just give up, but like I said, I have never felt like this about a girl and I think we are perfect for each other. I was thinking of taking another shot around V-day, but need to figure out a way to increase my chances.