you're 15.......chill out lassie an don't stress yourself about relationships at that age, don't put either of yu under any undue pressure....relax, let nature take it's course, he's probably as anxious as you are
you need all your friends to see you're together.. really, that's not how it works. be happy with what you have and stop worrying about proving things to other people.
maybe he just wants to sit normally? its probably quite new to him too, if there is a lot of pressure about this the relationship may be short lived. you may feel the need to show you are a girlfriend to the world, he may not share that need to do everything publickly.