Left handle bar won't tighten...

I have a 09' 750 the front tire went off the sidewalk a bit while trying to push the bike into the garage. So I grabbed it by the bars and pulled it back up, when I did the left handle bar just went limp... completely loose so I inspected it and it's not broken. So I loosened the bolt, and slid the bar back up and into position. I tightened it all the way down, and then when I leaned on the bars it just loosens right back up... not sure what's happening and I am a complete noob. I just bought the bike, and I have never done anything to a motorcycle mechanically...I'm not sure if I'm just putting the bar in the wrong place, or what is going on. I straightened up the wheel and tried to position the clamp at the same angle that the throttle side is positioned at, I pulled it all the way up as high as it would go.