I see it differently.

I think that you can love someone with all of your heart but they still may not be the one. That doesn't make you a bad person. In love there are no guarantees. Just because she fell in love with you (but I get the feeling that you may not have quite the same feelings for her) doesn't mean you're a bad person. It happens all of the time.

Don't string her along if your feelings aren't there. Don't listen to everyone else who tells you that you should marry her. (Bad idea listening to what others think as they don't know the inner workings of a relationship!)

Since you're so inexperienced, I have the feeling that you think that because everything seems right on paper that this girl is perfect for you. Unfortunately, it doesn't work like that. If the feelings aren't there, the feelings aren't there.