great advise Fern! you got such a super deal on the dress, why not see if you can do as good for a tux. If not, a nice dark suit will be just fine.If the dress makes you feel pretty and it looks good on you, go for it!!
little tip: wear the dressier of your formal outfits on the first formal night. The Captain's Welcome Aboard Party- its the dressier of the formal nights.
Can you post a picture of your gown?