You did everything just right. NEVER get out of your vehicle, always call the police. Telling him to back away was also the proper way to handle the situation. Infact, you did everything you should.
I worked for an insurance company for many years and saw reports that would scare you to death. Women who were grabbed out of their vehicles and killed. It isn't always car jacking, sometimes they want the lady in the vehicle. Mostly women who were at shopping centers. I believe shopping centers are very dangerous. These men drive up so close to the opposite side of a woman's car that she can't get out. Then they get in the vehicle on the other side. They drove off with one woman and took her to a farm and killed her. They found her body in a field.
Also at Christmas time women will have their hands full and not even notice someone behind them following them to their cars. Always be sure you are not being followed and go back into the store and get help if someone follows you. But, I don't need to tell you, you seem very able to take care of yourself. KEEP UP THE GOOD WORK!
Psalm 16 1,2,3
Preserve me O God; for in thee do I put my trust. O my soul, thou hast said unto the Lord, Thou art my Lord: my goodness extendeth not to thee; But to the saints that are in the earth, and to the excellent , in whom is all my delight.