Let me straighten this out. Post a [real] screenshot of your final score if you have it.
but I should say that it is impossible to get 100%, because we programmed the game that way.
The reason is, nothing is 100%. Especially zombie survival odds.
And besides, if you shot a "bunch of zombies" at the police station, you will have had point deducted for the effort, you see the point is not to kill as many zombies as you can, but to escape to safety, and shooting zombies creates unsafe conditions.
Sorry - Ed