You are going to have to open it up to see what it actually has. I'd expect to find a small switch mounted so the actuator is hit by the tube when it is fully retracted, and maybe a similar one on the other end. If you can push on the switch with a pencil, finger whatever it should stop the motor while it is retracting. If it does then you probably have a mechanical problem where the switch isn't pushed before the tube hits a stop. If it doesn't stop the motor then it is likely the switch is bad.
The other possibility is that it has a rotary potentiometer sensing shaft rotations. If that is the case you may find that the there is away to adjust the rotation, or there may be trimmer pots on the circuit board that adjust the position.
Of course there could be an electronic problem, but this kind of problem is generally likely to be switch or potentiometer related.