Jeans and a Tee. Put your hair in a pony tail. You won't fail.
Well, since its a concert, maybe a band t-shirt with a nice pair of jeans and some flats? Or, if it'll be cold, you can never go wrong with la
Best of luck, and I hope you have a good time :)
Be yourself.....if you want to look cute yet be comfortable, that's how you should dress. Don't over think this.