fuel tank

i recently started to smell a gas smell when i sit at light or if i leave my car running somewhere, thought it was strange until the other day i was coming out of the gym after leaving my car running i noticed a leak coming from the rear of my car, so i smelled it and it was gas so i cut my car off and checked to see if i could see any damage to the fuel tank, no damage but noticed a plug or screw missing maybe problem need help :sad: