Hospital band

So when it was time to leave the hospital three months ago when I had my babygirl. They cut the band band that was on her life leg and after they took it out it’s was purple so I asked the nurse and she said it’ll go away. Than on her two month check up it was still there. And the doctor said it’ll go away if not than it’s a birthmark and I’m just like she didn’t have this when she born. Than when they put the band and after the cut when it was time to leave it was there. Another month passed and still there. It literally looks like hit type of mark