Yeah, Man. Take him back. Shame on the LFS for misguiding you like that. No offense, but shame on you too for pruchasing that fish without researching first (slap yourself on the hand. LOL). I can say this because, it's how I started too. Almost identical experience, but my purchase was Koran Angel from my LFS that only wanted to make a sale. I felt ashamed because I knew better.

I'm sure we all have slipped up in some way or another. LOL...
Honestly, the LFS is probably waiting for you to return the fish in the first place because they either mis-informed you, or were not experienced themselves. As mentioned above, not only is the fish not reef safe, but it gets VERY large. Where are you located? Shop around until you find an honest and knowledgeable LFS. If you can't find one, live aquaria is great. Also search this forum as there are very knowledgeable people here.
Last, but not least: Is this fish in a QT? If so, he'll be easy to remove. If not, have fun getting him out of your reef. LOL.
Seriously, though: Set up a QT to protect yourself and your livestock. Aside from not being reef safe, how do you know this new fish doesn't have disease or parasites?
Best of luck, and keep us posted!!!