When my house was first built, the person who poured the concrete must have thought that I would never put in a garage door. So he decided to put a dip about four wide and about three feet from the edge closest to the driveway in towards the inside of the garage I guess thinking I would wash my car inside the garage and that way the water would run out. Problem is, I never intended to do that and I did eventually put a garage door in and now I am stuck with this gaping hole across the bottom of the door where it does not touch the floor. What would be the best way to fix this problem? Do I need to just use self leveling cement and pour it into the dip and allow it to smooth itself out? The floor has been painted so I guess I would have to use muriatic acid to clean the paint which I guess should also etched the concrete as well. Any ideas or suggestions?