As with any other cooking metal, as you use it, grease deposits will accumulate in the scratches or serface imperfections, resulting in a smooth surface. Lodge cast-iron is very coarse from the factory. Yet, when it's seasoned, the food jmust doesn't stick to it very well. And as time goes by, the surface seems to become smooth. I think that the durabilityl of casat iron makes it unlikely that my spatulas are grinding the surface smooth. rather, I think the little valleys are filling with grease, which hardens as heat is applied.
I think your griddle will work just fine as is.
Seeeeeya; Goodweed of the North