Hey don't worry about it. I did just about the same thing. After the int with just under 6mins to go (probably when you turned it off), I said "game over", and prepared to leave to go get my daughter. I stuck around for "just one more play", and you know what Urlacher did. My wife took a trip to the bathroom and missed the punt return.

You can't take anything for granted in this game.
Normal, smash-mouth football (12 play, 80yd drives, etc) is what, 99% of the game? Under those circumstances, Chicago wasn't going to win the game. It took dipping into that final 1% (which probably equated to 25% or more in this game) to pull off the win. And they did it twice (strip-six and punt return)! We'll probably never see that happen again.
Personally, I wouldn't have turned it off or left the stadium, because I've seen enough blown games to know that it truly isn't over until 0:00 shows on the clock. However, I saw nothing that would have indicated a comeback was in the works. The nails were in the coffin (at 6mins to go), and I was just waiting for it to be lowered into the ground.
Don't fret about giving up on your team, but do take this as a lesson to always watch a game from kickoff to 0:00.