Wood Floor Worn Spot!
When wood has been exposed to natural light over many years, it changes color. When it is sanded that color change goes away, and you have what you have now. I am surprised that is all the difference it is.

I would suggest "toning the finish", as in add color to the top coats that mimic what the aging has done on the surrounding surface. If the color looks grayer than the new, add a few drop of gray or black stain to the finish to give it a subtle difference. Put a coat of that over it. If it is heading in the right direction, add a second coat to add to it. If it goes the wrong direction in any step, use the solvent appropriate for your finish, wipe it all off and let it dry, start again. 

Keep the added coloring stain well under 25% of the volume of the finish. Stain weakens the wear ability of the finish. This why 2 coats of toned finish. Do not try to do it in one shot. If you get the right color and your added mix is only 10% of the total mix, good deal. Carefull how you cut in the new finish. You may have guessed that adding the toned finish over the existing finish will make a darker ring around your work.

DO NOT MIX oil and water based stains.