Oh no! Something similar happened to me with a Cartier ring that I got a while back. Fortunately, my SA allowed me to exchange it even though I'd worn it out of the store, so I got lucky there, and even if they hadn't, it wasn't a super expensive piece anyway. But from now on I've decided I'm not buying anything unless I feel good about the way it fits from the start. Over the years I've also had several experiences with Chanel bags where SAs kind of pushed me to accept/not return bags that had scratched clasps and other quality issues, saying that they were the last ones available, couldn't get more, it's not that bad, etc., and then I ended up selling at a loss and feeling lousy about it because the issues never stopped bothering me. It sucks to miss out on pieces you really wanted because they're not right for you in some way, but I learned the hard way that in the end it's even sadder to have spent so much money on something that was wrong for you when you had doubts about it in the first place.
You might consider asking your new SA if there's a resizing/remake policy like Cartier has, because that was what I'd originally planned on doing with the ring if I hadn't been allowed to exchange. If not, I think your best bet is probably selling. But if it makes you feel any better, by selling it, you might be helping someone who really wants it but can only afford pre-loved get the piece of their dreams, and it can go to a good home where it will be loved and cherished, instead of making you feel bad every time you put it on.