I made Justin tall and athletic because that is how the story describes him. I made Hannah look to be a "normal" high school girl because no one in the story expected this to happen. Everyone thought she was a normal happy girl.
I think Justin tries to be a nice person but falls into the peer pressure trap. He is more worried about how everyone sees him than how the ones that are close views him.
He is on Hannah's list because he hurts her in front of others and causes people to look at her differently.