The pilot of the retractable landing gear-equipped airplane reported that, during the landing roll, he inadvertently moved the landing gear position handle to the "up" position. He immediately recognized his error and moved the handle back to the "down" position. Subsequently, he saw the left wing settle slightly, so he added power and performed a go-around. Once airborne, he asked the tower controllers to observe the landing gear, and they confirmed that the left main landing gear was "canted inward" and did not appear to be down and locked. The pilot stated that, during the second landing, he placed the gear handle in the “down” position and saw the gear indicator lights were showing "down and locked." However, during the landing roll, the left wing settled onto the runway. The airplane sustained substantial damage to the left aileron. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.