1. If 2-3mm offset bothers you it's definitely worth correcting. Life is way too short to put up with petty irritations that are so easily corrected.

2. If it was my bike I'd loosen each of the 4 bolts exactly 1 turn and see it that was enough to slide your bar over (my bet, by the way). The trick on a 4 bolt clamp is to get all 4 bolts evenly torqued. I'd tighten each one just enough until I could start to feel some resistance. Then I'd go back around and snug up each one an equal amount. That procedure is probably overkill with a steel bar but not precise enough for a lightweight carbon handlebar.