Welcome aboard and congrats on the new 590!
Don't feel bad, same thing happened to me. I bought a 500 cruiser only to find out it was a 590 a few days later. Many gun store employees don't even know the difference between a 500 and a 590 and there can be a bit of ambiguity there.
We've got a great group of folks here on Mossberg Owners and the atmosphere is very laid back. The only thing we like better than discussing each other's guns is lookin at 'em, so be sure to post up some pics of your 590 and any other firearms you own in the various sub-forums. You'll find that we're into a lot more than just Mossberg around here. Let us know if you have any questions.
Enjoy the site!