Small-value current sense resistor value changes after assembly
Corroborating Kvegaoro, if the layout isn't ideal, you will not get the intended 60mohm. Also consider that the land pad and soldering quality will impact your measurement.

Consider that without a true Kelvin force/sense, you will not reliably measure 60mohm. The resistance of the probe leads will be at least that much. 

You can attempt to create a kelvin setup by soldering some wires right at the SenseAmp pins and force 100mA and then measure the voltage drop. Do the same for 200mA. The slope is the actual resistance.