Here's the final image. I'm using a "pixel zoom" value of 7.0f (see below).:
float x = 2.f * (j - xres/2.f + 0.5f)/xres;
float y = 2.f * (i - yres/2.f + 0.5f)/yres;
"2.f" is the "pixel zoom" value. When I ran my program using these values, this is the image I got:
This is still the same image, but super zoomed in. I don't know if this is what we were supposed to have, but I changed my picture above to be a little more pleasing on the eye.