Probably not, if it actually works.
*unless you haven't downloaded it, might still be a chance.

If you have not downloaded it, GOG refund is really quick.

I did downloaded it. No chance for trading, or tickets, no...

Would suggest trying anyway, might as well ask them.

You are not eligible for a refund if you have already downloaded it and it works...

...but it doesn't hurt to ask, if you have a good reason and they believe you (buying a wrong game in mistake might be a good enough reason).

For instance, I did get credit back when I accidentally bought a vanilla version of X Rebirth, when I meant to buy the X Rebirth Home of Light Complete Edition (and I didn't want to have to buy the Home of Light upgrade because getting the vanilla game + upgrade cost much more than buying the complete edition right away).

And yes I had already downloaded it too. Anyway when I explained that I really meant to buy the complete edition instead, they refunded me in store credit and removed the vanilla version from my account. Then I later bought the complete edition.

If it's entirely the wrong game, rather than the wrong specific edition of a game, it's a bit hard to believe that it took checking it out, paying for it, downloading it, installing it and actually playing it before he noticed it wasn't the game he actually intended to buy.

But of course, GOG believes all their customers are too stupid to download Galaxy if they want to use it, so they may believe the story.