People and men get bumps on their genitals all the time. No reason to be embarrassed. Doctors are the best one to show it to. How long has the spot been there? Remember, the penis can get a bruise on it. Any bumps or injuries lately? Otherwise, I thik you should show it to your doctor. There is something called Purpura. Here is information on that: Purpura, also called blood spots, appear as purple or reddish blemishes on the skin. These spots are not a direct result of an injury to the penis. Instead, purpura is often the symptom of an underlying condition.
Some possible causes of purpura include:
bleeding or clotting issue
medication side effects
inflammation of the blood vessels
Not meant to scare you. Most things are able to be cleared up if they are the culprit. But get checked out by your doctor just to be safe. https://www.medicalnewstoday.com/articles/320963#causes