Check the boat out of the water for steering. If it moves easily, you are OK. If the boat pull strongly to one side, you can adjust the trim tab to offset the pull. You still will have torque steer due to the rotation of the prop against the water.
The horizontal fins prevent ventilation - sucking air around the prop. The bolt on fins allow the trim of the motor to exert more force on the motor housing. Kind of like a wing. It make trim more sensitive and the boat will get on plane at slow speeds.