Looks like you have the "tool center" programmed in the feature? If you use tool tip, then it will look like it stops. If you need tool center, then you may want to offset your boundry by that cutters half.
Also, for your boundry, it looks like you have "drawn it" to try and be close to where you want it to stop. You can get a more exact boundry by extracting the edges of the surface/s you are cutting, then create a flat plane up above Z0 and then project those edges up to the flat plane. An exact boundry.