Just judging by the collar, where right below the Equipment NFL shield there's a flash of green where there should be yellow in the collar, I'd say makes this a fake. Also, usually the little NFL guy on the jock tag doesn't quite look like the real one in key areas (the ball, the guy's leg is straight where it should be curved, and his posterior is rounded where it should be at more of an angle). Also, the numbers look rather glossy. Typically, numbers on genuine authentics look a tad more dull.
Sorry dear, I hope you didn't pay too much for it. Overall it's a nice enough looking jersey, spare the snafu on the collar.