How do i get over my ex crush ?

I'm a 20 yr old guy. When i was 16 i had the BIGGEST crush on this girl who rejected me harshly. Back then i was very short, had bad acne, was very skinny and just generally bad with girls. This girl was in my cl so i decided to ask her out to lunch one time after i'd spoken to her. In response she just walked away and told everyone in my cl about my crush. I was devastated and cried for months. Over time it became better but my feelings haven't gone away. I have changed physically, worked out in gym and grown up for the better and will be seeing her tomorrow. So how do i behave when i see her ?