Relax! You've had it a week. You're pounding away on it, trying everything out (good - you should be!). My first week, I got 4 - 5 hours, too. Then I calmed down and settled into more normal use. And I reduced the brightness a bit. Now as I type it shows 58% charge and 5.21 hours remaining, which is about what I would expect.
Give it another week or two and see where you are. (You have a year's warranty, even if you didn't buy AppleCare.) If you are still concerned then, take it to Apple. But I will bet by then you'll be on to worrying about other things (at least, that's what happened to me!)
Cheers!