I was told I couldn't get my bellybutton pierced because I have a longer than normal artery.is that true?

The placental flow of blood and nourishment came to you from your Mother through the placental cord, entering you through your navel.

But after you were born, this artery/vein system was no longer needed, and withered away.

There is no significant artery close and shallow to your navel, but anyway, a navel ring would probably be placed in the fatty tissue near the navel, not through the navel itself.

This question may be safely be discussed with a health professional such as the practice nurse or doctor.