Your sunroof may be slightly out of alignment. If its not positioned straight on their guides, your sunroof will only retract so far. Troublshooting an electrical sunroof is difficult because there are very few mechanical or electrical components that are easily accessible. Unless you have a good mechanic you normally visit, you may need to have it checked out by a Mitsubishi dealership. Because of the age of your car, they may opt to just replace with a new one. This will NOT be cheap. It may be as simple as the guide track being re-greased, but have it looked over by a professional.
Good luck!