Anyone else have experience of margin below 5mm?

My pathology shows lymph is clear but the cancer cells were on the move in the lymphatic vessels (I assume leading up to the sentinel node). 

The surgeon said they got a clear surgical margin. However, I asked for a print out of the report and on reading it read that the margin agains the chest wall was only 3mm which seemed a fine line to me. So I read up and the first NHS guideline document I read said 5mm is the guideline. 

I qualified for the gene test and now wait to see if I am high or low risk of recurrence, to inform treatment plan beyond the guaranteed requirement for Tamoxifen.  Wherever I am on the scale I am concerned I could be one of the 15% of women for whom cells have travelled undetectably in the blood.

Any experience of a less than 5mm chest wall margin among forum users, and treatment advice as a result?

Your feedback would be much appreciated. If nothing else it will help equip me with questions I can ask the oncologist when I meet them on 22nd Nov (7 weeks after my op, which seems a long time to wait)