You did put the pizza on a rack in the oven and not on the base under which the burner sits, right?
Get an oven thermometer (a cheap mechanical one should do fine) and see what the temperature is vs. the set temperature on the dial. You can then convert manually as needed, or often take the oven control knob off and adjust a little screw on the gas control valve behind it to get the temperature calibration closer to correct. It sounds as though it may be too high.
I've heard good reports of putting something like a pizza stone or a suitably sized unglazed ceramic tile in the bottom of the oven to add some thermal mass and help even out the temperature.