Well, the correct method is to tell us your leadscrew pitch & whether you are microstepping or not, we can then tell you what entry you should make for the 'steps per unit' setting in your CNC app, but in the absence of that info, if your 'steps per unit' setting is set to 200 at the moment & you are saying that a 100mm piece comes out at just 80mm then increase the steps per unit setting to 250 & that should see a 100mm piece come out at 100mm