Hey Brent,
if you do this with a g-code toolpath, you will always have a portion around that you don’t reach, because the CAD/CAM software will take the bit diameter into account. The best way would be to use the gamepad and to jog around. This way, you can go to the very limits. You could first use a v-bit and mill with shallow depth (and this way you can check if the machine is squared).
See also this ← for how to achieve maximum workarea with a g-code toolpath