Everything is related to the ThingMark, you have to have the scale right in ThingWorx Studio or Creo and the real world. So, when your printed ThingMark is 170 mm across, you have to add 0.17 as your scale of the ThingMark in ThingWorx Studio. In Creo you have to measure the ThingMark and calculate the scale by hand. Just to mention that in ThingWorx Studio all the dimensions are in meters. The rest of the scales can be 1.
Above should work, as I have used it many times now.