I’m trying to refinish a vanity and chair and match what was originally used as finish. Seems the more I sand it the darker it gets, note bottom stool shelf.

The original color of finish was almost exactly like remaining color which is what I want. I must not have sanded the rest as much as the bottom shelf?

Any idea of the word type I have here and how to achieve a uniform look, matching the bottom shelf to the rest of the stool? Ty!!