My Header and Content area are not quite centered with each other.

I have gone through my CSS so many times to try and correct this, but I just can’t seem to get my header and content aligned together and in the middle of the page. I want to have the header and content area perfectly aligned so that the gray borders will only be on the left and right edges. I plan to make the header a different color and when I do that right now you can see that it is not aligned.

Any help would be greatly appreciated.

My site is asharpguitarinstruction.com