Vonbag, you admit you were not in the jumpseat of the flightdeck, but ignore what has been said!!!!
I am a Boeing 737-800 pilot, I also fly the 300, 400 and 700 version.
If you enter the runway, intending to expedite matters, you can stabilise the engines at 40% N1 as you turn on to the runway, then by hitting TOGA, that is the switch on the thrust lever to initiate the Take Off (or GO Around), the Thrust Levers will start to move to the selected takeoff thrust, of course the Autothrottle has to be on.
This takes a second or two, and the spooling from 40% N1 to approx 80 to 90% N1, takes a few seconds more. In this time it is quite possible to line the aircraft up nice and central. It sometimes can be refered to 'taking her on the roll'.
But then I am a mere airline pilot and not as knowledgable about such matters as the passengers, any time you wish to land the aircraft, be sure to let me know, I will of course let you know where you are going wrong with Themodynamics of fluid machinery.
FC