The pilot of a float-equipped airplane reported that he planned to step taxi while making a left turn, and then takeoff. He applied takeoff power to get the airplane on step, then reduced power, and started a turn to left. The airplane turned to the left sharper than he anticipated. He applied right rudder and reduced left aileron. As the turn started to straighten out, the airplane’s right wing struck the water, sustaining substantial damage. There were no preaccident mechanical issues with the airplane.