I am missing two critical components for this Flash: keeping the Zerglings inside the boundary (they all seem to run away), and making them explode when they are "shot" by the Marine.
All in all, it works like it's supposed to: the Zerglings wander around randomly unless they are being chased by the Marine, who will try to shoot them if he gets close enough. Also, if either the Zerglings touch the Command Center or the Marine goes too close to the Hive, they'll get evaporated. If the Marine gets killed, game over!