That's nothing. The guy who was claiming it was big in the promos was the freaked-out underling. The guy they had playing the head of NASA was much calmer.
Now, when I say that the asteroid was "nothing," keep in mind I'm talking on a global scale. It's true such an asteroid could cause earthquakes at about 6.9 on the Richter scale and destroy a city. But on a global scale, nothing major would happen. The Earth would keep spinning and the human race would survive. It would not be the end of the world.
For more information, and your own asteroid fun, check out http://www.lpl.arizona.edu/impacteffects/ where you can plug in your own asteroid and watch it destroy the Earth!