My [20F] gf [18F] doesn't feel loved by me and feels like I prefer other people. How do I make her feel loved?

Me and my girlfriend have been dating for a little over 4 months and recently she confessed that she feels like I prefer being with other people and when, while comforting her, I said "you know that I love you?" she shook her head. I love her and I enjoy spending time with her more than anyone else, if I had to pick between her and anyone else I would always pick her. But if that's how she feels I'm not sure what to do. We're pretty busy right now with studying and will be for the next couple of weeks and so there's not much free time, but I try to spend as much of it as I can with her. How do I make her feel loved?