Any cute Dress ideas for a plane?

So i have a 14 hour flight to out of the country, and I have to dress up because we're flying stand by. Which means my uncle wants me to dress up to represent the airline I guess. I have a skirt I was planning on wearing, because I didn't have time to go shopping before we left. We're spending my summer with my grandma in a different state and she doesnt have any good stores. my mom is coming up a few days before we leave to take us shopping and get us ready, and i'm going to ask her to take me to a store to buy a new dress. since the flight is 14 hours I want something that's comfortable. I sit on my legs if i have to sleep in a chair so nothing to short. I'm going to have a pair of knee leggings underneath so i don't flash anyone, but I'd like it to be somewhere close to knee lenght. I'm really into the Demi Lovato style and Selena Gomez style. i like to shop at forever 21, and things like that, but i dont want anything really girly. If it could be something that covers my shoulders, that'd be awesome too. I try to find clothes that cover my scars from self-mutilation. I don't really want to buy a cardigan or anything to put over my shoulders, because if it gets hot i'll take it off. I just need it to cover the scars on my shoulder. Links would be awesome Thank You:)