How do i build a "best friend" relationship with her?

in the middle of the 7th grade year (this year) there was a new student coming to my homeroom that i had to show all around the school. she's really cool, has my type of personality, sits next to me in HM, doesn't care what i look like (i have acne, it's hereditary!!), and we really enjoy talking to each other. i want to have a best friend relationship with her. i don't want to be like, hey give me your # and email!! i've only known her for about 2 months!! we're in the same algebra cl in the morning, and we talk to each other on the way there. we can't choose our seats, we get igned. and all we do is solve stuff. how do i get a better relationship with her "best friend" wise?