OK, I am late to the party, but I just acquired a new 10-inch pre-seasoned cast iron skillet. Directions said to rinse it out with very hot water, which I did. I didn't dry it thoroughly enough, and of course there soon appeared a blotch of rust on the pan surface, which I was able to rub away. Now, the pan surface where the rust was is a lighter color than the rest of the pan. Have I totally ruined it?