Sorry for the late reply (I thought the thread died).
So the way your describing it makes it sound like I would need to make a 2d array that holds every coordinate possible for the whole screen and then when drawing the bullets it would add one to each pixel that it hits and then afterwards I can just pull up a screen that shows the total outcome.
Now would it be smart or efficient to look into a way in which when I run the program I can have another screen pop up and that one will show just the heat map? The other way I could do it is when I press a button it will pause the game and show the heat map.