Changing switch

I am trying to change a light switch that controls an outlet. I thought it would be as simple as disconnecting the old switch and then reconnecting the new one with the same configuration. I must have done something wrong. Now the switch seems to control Every light and outlet in the room. The old switch had three black wires connected to it, one of which was hot. The neutral wires were connected with a wire nut in the box, nothing connected to the switch.