the screen looking off center is probably due to how the screen is seated in the white plastic guard surrounding it. i've noticed this a lot... there is enough wiggle room to push it to one side or another enough to notice. next time you've got it opened, move the LCD a little bit and see if this helps. a gentle nudge.
To add! With pretty much any backlit screen that requires you to cut out the left-side of the plastic guard, if you cut off too much and happen to hack off the plastic aligning pin/dowel as well, it can lead to the screen being mounted at a bit of an angle. If you cut the plastic and leave the aligning pin/dowel, it should center up pretty well.