Dance Outfit! Help!!?

For our christmas dance, it will be way moe formal thatn a lot of dances! But its a junior high dance! meaning 7th and 8th grade! I'm in 7th and the shoulder straps have to be like 1 1/2 inches wide but a lot of people (me) lol break that rule go in with a jacket then take it off when they get inside. so does anyone know of any good dresses that they found online?! please help! send the link! thx!