55Jlz is newly diagnosed please offer her the awesome support that you all do.

Hi @55Jlz Ditto what @romla and @kmakm have said.  It's normal to be nervous and that day of admission is a long one - you might be better with some good magazines rather than a book, though - I found it too hard to focus.  I don't know about you but I'm never good going under - I always get anxious.  I was so nervous by the time I went into theatre that the surgeon held my hand to calm me while the anaesthetist put the drugs in.  Do try to take things one step at a time.  You will see the surgeon, of course, you will have some pre-op scanny things done with markers, you will probably see a breast care nurse each day and get information and goodies (awful Brunnhilde bra).
This op will determine exactly what's going on.  Once the surgeon goes in, he/she will be able to see the real size of the tumour and take the sentinel nodes.  These will go off for biopsy and the report that comes back will be the one that gives you the full information about the cancer.  In my case, with the sneaky monster, lobular carcinoma, the tumour was twice the size they thought and had gone into 3 nodes (all previous tests indicated that the nodes looked good) so, given the surgeon could not get clear margins and I had to have more nodes taken, I went back for a full mastectomy and axillary dissection.  The progress from there is about recovery for a few weeks, then, if you need it, you will be referred for further treatment, whatever that plan will be.
So, focus on getting through the surgery - get yourself a comfy short sleeve, full button pyjama top if you can as it's much easier in hospital.  And my personal tip - if you like swimming, do it now because you won't be allowed to for weeks!