I also had to have two surgeries for a small breast cancer, because margins weren't clear after 1st op. My surgeon told me that it's hard to distinguish where a tumor ends, although I think they have ways of testing during the surgery. But, they have to rely on post-op biopsy to be sure they got it all. My 2nd op produced "no ink on tumor" as biopsy result--meaning (I think) that the margins were minuscule, though clear. I would have been happier with clear margins of a couple of millimeters--even if that meant a 3rd surgery. But my cancer center (MSK) was satisfied.

Regarding the surgical scar--it looked the same after the 2nd surgery as it did after the 1st. The surgical scar is less disfiguring than the scar made by the biopsy "gun". That left a big dent in my breast that hasn't filled in.