Princess's formula for calculating single fares usually works this way.
1. Subtract the port charges from the published fare to get the real base fare.
2. Multiply by the real base fare by the single supplement factor (150%, 160%, or 200% depending upon itinerary and class of cabin) to compute the single base fare.
3. Add the port charges to the single base fare to get the regular single fare. This should be the quoted fare.
It's possible that the fare to which somebody added the port charges in your worksheet already had the port charges removed.