First Timer Mistakes...need advice
So...there was one small spot on my floor where the poly or more likely shellac had come up after an aggressive deep cleaning. My landlord told me that I could just sand around the area and cover it with a poly and it would blend in. Well that one sanding spot became a much bigger patch as you can see. I used an orbital hand sander on the area to remove all of the finish and I was cleaning off the wood with mineral spirits and noticed all of this texture and spotting. I know that in some of the spots I dug in too hard or angled the sander which caused the grooves (picture 2), but I also noticed these dark spots in picture 3. The texture of the wood that you see in picture 1, feels soft, but looks like it should feel rough.
What have I done and how can I fix this without bringing in a pro? I am a renter. Any help would be much appreciated. Thanks so much in advance for not being mean or unnecessarily critical.