Emg report say the sensory nerve conduction amplitude in the right lower limb were on the lower limits of normal. what does that mean?

Means it's normal: Low or high end of normal is still normal when it comes to that sort of statement on an EMG report. If, however, the clinical situation were explained a bit more or if there were other EMG's you've had in the past that show a distinct change from these results then, there might reason to question the stated "normality." Otherwise, be glad you're done with the test! Good luck.