Dan,
That is what I teach for sail trim. Line up the points of mast base and sheeting center, trim so the sail is slightly off center of mast and mark the sheet. That way you know exactly where to sheet in after any maneuver, i.e., tack, start, mark rounding.
At least you are in the ballpark. In a puff, sheet in a bit more, in a lull, ease off a bit.

You certainly do not want to oversheet a square head, or any other sail for that matter.
Rick