The temperature fluctuates between 65 and 72 degrees C, is this normal?

It is normal for the temperature to fluctuate a little when the mat has reached the set temperature. That happens because the mat heats up to a little higher level and then stops to heat, so the temperature decreases a little, and then it resumes heating again to achieve a little higher than the set level and so on. It is the standard operation of a thermostat-type device.

If you change the mat Thermo insulation condition, for example, stand up from the mat or remove the blanket and protector and let it be uncovered for 5 minutes, the temperature may drop 20 C because the hot crystals will radiate heat away fast. They will get warm to the touch, and even though the temperature indicator on the controller will go up to 65C again, the mat will be only slightly warm to touch unless your cover it again or lie on it.