When a nozzle is in the filler neck, that little "flap" is depressed anyway, so it being bent isn't going to affect whether the gas stops or not. The pump/nozzle will kick off when the end of the nozzle becomes submerged in gasoline, the resistance it causes to the fuel flow is what clicks the automatic fill off.(Remember this, so that next time that f#cker keeps kicking off every time you set it, pull the nozzle out an inch or two and start it again, the fuel isn't flowing down the filler neck quick enough, it causes resistance and kicks off, so giving the fuel more space helps remedy the situation.
Now, some filler necks on newer vehicles have another flap further down in the hose that is on a center axis, these are what prevents most people from shoving a hose down in your gas tank and siphoning your hard earned gas out.
So, forget about the stupid flap up at the top, infact, on my jeep and my mazda truck I ripped that f#cker out so I could use a gas can without the **** spilling out.