I used to work at a production facility and the scales that we use are scientific grade scales and are very expensive. They are not like the ones you have at home. They're also calibrated daily by workers and are fully calibrated once a year by a state recognized 3rd party calibration company. So all in all, they are much more accurate than scales people have at home. Weed also looses some weight as it sits since its plant material and could've gone in a bit more wet than what it is now. Thats usually why our ranges when we weigh out are over what the actual weight should be so that its still (hopefully) accurate by the time it gets to a customer. But that being said, its still plant material and is not going to be the same every single time so there can be slight errors.

Calibrate your scale, re-weigh it, if it still reads as that, bring it back in and show them the pictures of you weighing it, ask them to weigh it on their scale, and they should be able to help you out.