welcome to the Forum, GOOD information above, a lite "tap" with a plastic hammer on the top of the screw driver as you try to turn the screw, may help............
By the way , is the rear sight blade "centered" in the slot or already all the way over to the left???? If you are right handed and may have 'short' fingers, you could be pushing the gun ever so slightly to the left, if the trigger finger is too long, ,may "Pull it to the right"....we like to actually "see" just what is going on when someone else is firing the gun....many years ago the NRA provided a "card" that shows how to "read" a fired target by the hole pattern...........helped us when working on guns at Camp Perry back in the 70's at the National Matches........
".... 'splains a LOT...."