Hi Elizabeth congenital melanocytic nevus has a potential of developing cancerous change. 3cm nevus with atypia is certainly a cause of worry. Is it growing or stationary? Wat is histological report? Early surgical excision is recommended in rapidly growing CMN. If its stationary you can wait for few months, Other treatmnet are laser ,cryo surgery, dermabrasion. If you can mail me photos and answers at email@example.com TaKE care.