After 2-3 min, when the bottom of the omelet gets brownish, use a kitchen spoon to fold the omelet twice. First from the closer end towards the middle, and second towards the far end of the pan. There's no need to flip the omelet, just fold it. Even if the upper side of the omelet seems uncooked before folding, the "inner layers" of the omelet will get done by the end of the process.