Your tank looks great .

You could move the heat pad to the outside side wall for safety. Be careful to remove it very slowly so the inside heat coils to not break. They are very delicate. The other safer option is to buy a small fish tank submersible heater with a thermostat built in and you can place it in under the gravel where they will not burn themselves. Be sure not to turn it on until its under the water. They work great and you can set the desired temp .