Homebrew PCBs

Keep in mind, the average laser printer (including yours) is 600 DPI -
that's 1.33 mils PER PIXEL.  An 0.5mm pitch part has pads on the order
of only six pixels, so "off by one" is a 16% difference.

Som postscript printers "fill" a region by drawing both the outline and
the fill. That tends to produce features that are one pixel larger than
you expect.  gEDA's PCB has a setting to compensate for this if needed,
or you can use some other program to convert the output to a 600 DPI
bitmap, preview it, adjust if needed, and print the bitmap.