I don't understand your problem here. You have said that you feel there are a large number of fish in these tournaments and from the flop you have (correctly) placed your opponent on Kx, and doubed up. You felt previously that you weren't being bold enough when you felt you were ahead and here you backed up your belief.

However, I don't like continuation betting into a field of 4 players early in an SNG for the same reason that I don't think you are wrong to go all in on the river - namely that players with either 1st or 2nd pair are likely to call.

I would limit continuation betting or bluffing until either the blinds go up, or you are in a 2 way pot, preferably with someone who you know is capable of laying a hand down.