Do i have to call someone my age uncle?

im 15 and a freshman in high school. my grandpa and i are really close. we lost my grandma to brest cancer when i was 10 and then he met laurie. she is amazing! i love her and she is going to be an awesome step grandma. but she has a son who is 17 and a junior in high school. we go to the same school, but our schools really big theres 4100 kids. he is actually the quarter back on varsity and im a freshman cheerleader. weve never talked before untill laurie started bringing him around, and now she wants all my grandpas grand kids to call her son uncle after they get married next weekend. i really dont see why i should have to.. hes only 2 years older then me and he isnt really my "uncle" but i dont want to make the family mad and i also have alot of little cousins that are inbetween the ages of 2 and 10, so i dont know what to do and if i do call him uncle can it just be at family things and not public things because id find it embarissing i mean he is really cool though and said hed drive me around whenever and to school and stuff, i just dont know what to do!