congrats on the first day! When i was in high school I was one of a hand full of "those punk guy's", complete w/ mohawk, spikes, painted leather jacket, etc., etc. So I have never really cared what other people have thought of me, so I am lucky in that aspect.
But the point is if you walk around in a kilt with the attitude that you own and rule the world, that is all the confidance that you need. Trust me if you walk around w/ that kind of attitude, nobody will muck wit' cha! (even if you wore a full evening gown complete w/ tights and pumps!!, well maybe not pumps but you get the pic.)