I suggest you see an oncologist surgeon, because dermatologists tend to underestimate dangerous lesions. I lost half of my nose due to an irresponsible dermatologist; I needed a Mohs’ micrographic surgery. Please consult an oncologist. Also, using a larger margin will not cause problems...
"Mohs’ micrographic surgery might prove useful for excision of melanoma, especially lesions located on the head, neck, hands, and feet. However, there are no formal recommendations pending additional studies.4 Studies suggest that the current recommendation of 0.5-mm margins for lentigo maligna (melanoma in situ) is often insufficient. Mohs’ micrographic surgery and margin-controlled excision of lentigo maligna offer lower recurrence rates and allow tissue to be conserved."
I have found another interesting reference:
Lentigo maligna is treated with definitive surgical therapy. The actual margins of atypia usually extend beyond the clinically apparent margin; total removal may be difficult. National Comprehensive Cancer Network (NCCN) practice guidelines for melanoma in 2006 are as follows (tumor thickness, recommended clinical margin):11
Tumor in situ, margin 0.5 cm
Tumor less than 1 mm, margin 1 cm
Tumor 1-2 mm, margin 1-2 cm
Tumor 2-4 mm, margin 2 cm
Tumor >4 mm, margin at least 2 cm