Isn’t that what it’s designed to do?
Overscanning generates extra moves, past the ends of each line, switching the laser off before it fully stops, or even before it begins to decelerate, allowing the entirety of the engraving to happen at the desired head speed and then decelerating while the laser is not burning.
It’s not clear what your problem is.
If you are missing your start and end points, on a machine like that, it’s more likely to be mechanical slop.