Soooo...what kind of Mercedes are we talking about here? A used sedan for $25k or a brand new roadster for $100k? I think this will determine your path forward. If you bought a cheaper and/or used model, it might make sense to keep it until you break even or long-term if you can ensure that you will drive it for a decade or more. If you bought something super expensive, then I advise that you sell it as soon as possible. You'll need to do some research to figure out the best approach for doing that, namely, how much do you owe, how much is it worth, if you're underwater how you'll pay for that, can you get around without a car for awhile, when you do get a new car what is a reasonable replacement, etc.
More generally, what's done is done. You know this wasn't a good financial move. Instead of perseverating on that fact, make an actionable plan to improve the situation and think through what you'll do in the future to avoid another situation like this.