Chances are if you start tightening the screw the pot is just going to spin in place until the wiring binds or you break off a pole. If your guitar has a pickguard I recommend taking the pickguard off so you can atleast get a pair of pliers around the pot to keep it steady. Then you can tighten the screw down as much as you want without the pot spinning. One thing you can do to keep the screw from coming undone is to put something like hot glue or something over it to keep it from gradually loosening. It's easier if your guitar is rear routed... because you won't have to worry about the strings being in the way!