half-nose mask problem

I've had the half one mask on my ride for a couple of months now and I constantly have a problem with the left flap popping out at high speeds (80+mph). It flutters in the wind and is very loud as it hits against the bumper. I have tried tightening the bumper on the left side, but the bolt gets to a point where it keeps turning without tightening. Has anybody had this problem or know how to fix it?