Pick the object in Netfabb, it will turn green. you will also see the bounding box around the model. Does all of the model fit in this bounding box? Or as @mkroeker states 'is some very small part sitting some distance away from your model' making the bounding box bigger.
If the bounding box is the model only then the size shown will be correct. Do not use 'hundreds of millimetres' the size is in mm. So if the model now is 2 use 'Part - scale' type in 10 to make the model 20mm. The number you type in is a ratio of the original size.
Once you have scaled it you will have to export the model with the new size. 'Part - Export part - as Stl'
Last edited: Dec 26, 2013