The cement mixing and pouring went fine. I used something
called mortar "quikcrete" which we had laying around. I
leveled the new cement with a 2x4 and then water cured it
per the packaging directions, but then it seems to have
swelled noticeably while drying in the last 24 hours. The
new cement is no longer even with the surrounding edge. I
pre-fitted the shower base and I get a big of ponding. Is
there some kind of sander I could use to level the cement a
bit?

Pardon if these are naive questions. Making progress here;
learning things useful. :-)