Is that light brown bulb looking thing your seed potato? If so then you planted wrong. Your seed potato should be about 4 inches deep and as the plants grow upward you pile dirt on them. This is called hilling. What you can do is carefully and genty remove the entire root system and plant growth. Then remove all but about 6 inches of the soil and place the potato roots and plant onto the soil. Then cover up with soil to about 3 inches deep. As the plant grows add more soil.
If that brown bulb thing is not your seed potato it is a type of mushroom and is harmless to your plant.
I think you should have planted your potato deeper in the soil. You shouldn't see the potato out of the soil. I have grown so many potatoes in my gardens and my only problem with them is that they try to take over my entire garden by spreading without my permission!!! They choke out all my other veggies!!!