The end bottom tubes with crystals and the 1-2” on the left and right sides seem cooler. Is my mat defective if it does not get evenly hot across the whole surface?

All MediCrystal amethyst heating mats and pads use the same safe double silicon and Teflon insulated heating wires under several insulation layers and EMF shielding copper weaving. For extra electrical safety, the heating wires are positioned a short distance from the amethyst zone edges. So, the end tubes with crystals are heated indirectly by other stones. The longer the mat heats up, the warmer the end tubes and mat edges will be. That is why initially, you might feel like not all stones are equally hot. It is totally normal and has absolutely no effect on functionality.