You could remove all of the floorboards in the affected area and then nail them back down in a staggered fashion.
If you want an easy fix you could try to "inlay" a pattern that lloks intentional. For example, you can carefully cut out an area that includes the cut and is exacly the width of an inlay board. Then you could inlay around the room to make two rectangles. Or you could router out the area and lay in a thinner piece of inlay. You'll have to sand down everything afterward and do what you need to to avoid problems with the seasonal wood shrinkage and expansion.