Booth88 - first, do you have a handling charge on your shipping profile for the item that sold? or on a Package Preference that you entered? $1.50 sounds like a shipping and handling fee.
Second, do you have your calculated postage prices set for Retail or Etsy?
Third - the calculator is not integrated with shipping labels. These are two separate things. People using calculated shipping do not have to use Etsy labels unless they want to - they can go to the PO, they can print labels through PayPal or Stamps.com - anything they want.
Also, shipping labels have to be absolutely accurate. What gets calculated for an order can be off by a little - also, just because the calculator uses a certain box or envelope for your item, you don't have to use that. You still have to go through the steps of packing your item and weighing it before actually shipping.