What to wear to Confirmation?

I have my Confirmation coming up, and I'm not sure what to wear. I had already bought this dress (a href="http://www.dillards.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=301&langId=-1&storeId=301&productId=502435167&Ntk=all&Nty=1&splashlink=header_search&Ntt=Spaghetti-Strap+Pickup+Dress+&N=1000301&search.x=0&search.y=0&searchUrl=%2Fendeca%2FEndecaStartServlet%3FNtk%3Dall%26Nty%3D1%26splashlink%3Dheader_search%26Ntt%3DSpaghetti-Strap%2BPickup%2BDress%2B%26N%3D1000301%26search.x%3D0%26search.y%3D0&R=03401893&IN_MERCH=true)," rel="nofollow"http://www.dillards.com/webapp/wcs/store…/a but I think it might be too short, and I jus found out that I'll have to wear a white robe, where the black part of the dress will show up. Is this dress alright, or should I try to find another one?