my son had a fall a couple of weeks back, he hit his head and got a scrap down his face and a lump started to form in the middle of his head. I took him to the doctors and a few weeks on the bruising and the swelling have gone but theirs still a little lump underneath the skin.
Do not worry. It will take some time to heal but would eventually go away. You need not bother unless there are any associated ominous symptoms.