After all my hard work laying the floor, I chose a stain that ended up way too dark. I DID try it on scrap wood, but I must have applied it heavier, or something. Paint thinner and steelwool did not have any effect. I feel like an idiot.

I am going back to re-rent the u-sand machine(did a great job, by the way). I have put no coats beyond the stain.

Do I treat this as a normal refinish job? What grit should I start with?

thanks, as always, for your excellent advice.

well stain always looks darker over large areas, ALWAYS pick a lighter shade.
As far as fixing youre debactle(sp?) Tou dont have to do a complete resand, you should be able to just re final sand everything, then buff and stain, provided you are experienced enough with the sander to clean the wood with 100 grit paper