I Am Almost 20 Years Old. I Have Never Had

I am almost 20 years old. I have never had a baby or been pregnant. I have a horizontal line across my stomach right above my belly button. I have had it for as long as I can remember (probably about 5 or 6 years old.) The line makes it look like i have two bellies; the top belly is pretty flat, but the lower belly is big and hangs over my waist line. Why do I have this, and how do I get rid of it?