Now just set the jig up in your center hole on your keg. Put the tip of your plasma cutter into the hole that you drilled out on the jig, and start cutting.
In order to get the best circle possible, try to keep the motion smooth and slow while you are cutting. My jig didn't fit perfectly, so I just held it up to the edge of the valve hole closest to where I was cutting. I ended up with some pretty good results.
I quickly went over the edge with the flap disc to clean it up a little.