Go to a dermatologist and have it checked out. You'll feel a lot better if it's nothing.
I just went for a mole check a couple of weeks ago and had one suspicious spot on my back scraped. It came back as a melanoma, stage ia. I went back, had additional tissue around it cut out. I have a 99% chance of survival.
Don't take any chances with this thing. They do show up on toes, under nails, on bottoms of feet.