After reading your question, I was reminded of my wonderful college days. The feelings at that time were so pure. So, brother, cherish it. There will be no such pure feelings after work. As for what gift you give her, I think you should base it on her personality.
You have been classmates with her for such a long time, and you can't tell whether she is simple or likes to dress up. If you don't know what she likes, you can bribe her friends. I personally think that gifts should be given to her to suit her preferences, so that you can get twice the result with half the effort. What do you think?
So, you should observe carefully, give her a gift she likes, and express your feelings in time. I believe that she will be touched and will not refuse you. If you don't know all these, then give a safe gift, such as a bouquet of roses or a big doll. Both are fine.