Seems like a problem with many cars - quite irritating.
My 2003 Y34 M45
always stops about 1.0 to 1.2 gallons short of full at just about every pump. I have to manually stop/start a number of times (with "low-speed" filling) then to get it completely full. Not all pumps make it easy to hold the pump handle at just the right amount of pressure - some have ridiculously sensitive ones that always seem to gouge my fingers.
My wife's 2011 Acura TSX is far worse though. It stops about 3.5 to 3.7 gallons short of full!

In the recent past, whenever my wife filled up her car, she didn't have the patience to continue past the first stop, and then complained about "the mileage has gone down on the car" since she didn't get many miles out of a tank.
Needless to say, I patiently (but irritatedly) fill it all the way to the top whenever I get a chance to fill the Acura. Then the "miles per tank" miraculously recovers!
Z