Come on, come on, you know the drill by now, post your sketch, and updated schematic too if needed.
I think you are going to need new "state" variable which will take 3 values representing left, right and normal. This is in addition to the two state variables for left and right buttons you have now. When left button changes from not pressed to pressed and the state is normal or right, state becomes left. Similar for right button. If left button changes from not pressed to pressed and state is already left, state becomes normal. Similar for right button.