YTA.

While I personally think weddings are taken way too seriously and preciously, you have to ask yourself, "if roles were reversed, would I be mad?" That is often a good barometer but not always. For example because I don't care about weddings I would not give one flying fart if someone copied something from my wedding. If any thing I would take it as flattering that they liked it enough to use it too especially if I picked it out myself. However, knowing that I place a much lower value on weddings than others, I would know not to trust my own instincts on it in terms of social grace. You should really return the dress and find one that works for you. Or change the dress a little to make it your own. Add some frills and change the train or something Idk. Just make it more personal.

The nail in the AH coffin though was the statement about your friend not being able to be offended in person. That is never a good excuse. It's kind of like talking behind someone's back. It will reach them and it will hurt them. Either exchange the dress, change the dress, or accept that you will likely lose friends over it and hold the badge of wedding stealer. I think I've actually seen this episode on multiple sitcoms except the first wedding would've been cancelled so they stole it out of a dream journal thing or something. Idk.