With a cargo fire warning, you haven't got time to evaluate whether it's real or false. Evacuate! You certainly would not waste time taxiing to the ramp, even if they let you. Nor would you want to wait for mobile steps to be positioned at your aircraft. You might get a few injuries from the slide evacuation, far better then hundreds dying like in the cargo fire of the L1011 in Ryadh many years ago.
19 August 1980; Saudia L1011-200; Riyadh, Saudi Arabia: The crew turned back shortly after takeoff after a fire broke out in the aft cargo compartment. The aircraft was able to execute a safe landing, but the crew was unable to open the emergency exits due to the smoke and fire. All 14 crew members and 287 passengers were killed