Beautiful black boatneck formal evening gown

This is a brand new dress I purchased for my sister black tie wedding. I ended up going with a different dress instead. Absolutely nothing wrong with this dress, but I needed a navy dress. This dress is a size 10. I am usually a size 4/6 and formal gowns I usually fit in an 8, but this dress runs small. It is very long on me and I am 5ft 3in. I have only tried this dress on once. Never actually worn. I did remove the tags, but no alterations have been made.