Dark vein, belly button and down. I'M ONLY 13!?

I have a dimness line going from my belly button and down. I am lone 13, am NOT pregnant have NEVER have sex. What is this? How can I make it jump away? I've only see this on pregnant women and I'm scared... This is probably purely a normal oscillation puberty. I could not find anything specific. But it sounds like this would be more plausible to occur on a girl beside darker skin. Some down may be present along the line too. As long as everything else seem normal, I would not verbs.
"In the months and years following the appearance of pubic hair, other areas of skin which respond to androgens develop heavier mane (androgenic hair) in roughly the following sequence: underarm (axillary) quill, perianal hair, upper lip coat, sideburn (preauricular) hair, periareolar quill, and hairs along the linea nigra between from the pubic fleece to the umbilicus."
its very raw..i've seen abundantly of people own it..i have it too but its not that obvious..dont worry ur fine