A 38-year-old woman from Mumbai presents with a 4-month history of a pigmented lesion on her right calf. Excision with 5 mm margins and histopathology reveals superficial spreading melanoma with Breslow thickness of 1.2 mm, Clark level II, no ulceration, and mitotic rate of 1/mm². Sentinel lymph node biopsy of the inguinal nodes is performed and is negative. The patient is anxious about recurrence and asks about the need for further treatment. What is the most appropriate next step in management?