If you're training wrong, or not training hard enough, it doesnt matter how many sets you do. You won't grow.
Think of a stick of dynamite. If I tap on it with a pencil, will it explode? Probably not. If I tap on it 100 times with the same amount of force, it still won't explode right? .
It takes one, vehement strike to the stick of dynamite to set it off.
Your training is the exact same way. If your intensity (how hard) is low, adding more sets wont do any good.
Train HARDER. Realistically, you only need one, really good, really hard set to trigger muscle growth. .
Pull yourself up by the bootstraps and train harder man!!!