If I am not mistaken, lymph node involvement does not mean metastatic breast cancer. It was discussed at a conference and a patient advocate said the use of the word "metastasis" for lymph node involvement in reports is highly confusing (or alarming) for the patients and would be better if avoided. Do you think you can message your surgeon about this for a formal clarification (and relief)?
I hope all is clear after your mastectomy and wish you a speedy recovery, and a healthy life.