ROFL.. Oh MY gosh, I just laughed so hard.
Good news: It's grass!
Bad news:
That's CRABGRASS, dude. I'm currently battling it in my yard, because it grows everywhere and chokes out my flowerbeds.
What probably happened is a seed blew into your pot. The crabgrass came up, but your cannabis seed didn't.
Seriously, though, did you REALLY have to ask if that's a cannabis plant? Gives a whole new meaning to the phrase "let's go smoke some grass", doesn't it?