Hmm, well I would probably be concerned about a 0.3 mm margin too. Though can that even be that precisely? I hope you get a second opinion with an oncologist. It might be that rescreening and/or 'touch-up' surgery is appropriate. If so, I'd consider a different breast surgeon, and who specializes in oncology. I don't know if surgeons react to a patient's desire to have as little removed as possible or what, but I wanted, pun apologies in advance, a margin of safety. That doesn't mean that the surgeon didn't "get everything" by any means but a second opinion could give you some extra confidence either way. Maybe a vacuum-assisred wide needle biopsy can be a good indicator of whether further surgery is called for?