A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
What you don't mention is whether you've selected Justify in Format> Cells> Alignment - Horizontal Alignment.
Even with that applied, Mac Excel doesn't do Full/Forced Justification, nor does it support automatic hyphenation. Those typography features generally are found only in word processing/desktop publishing programs. It's unlikely that you'll get a razor sharp right edge to the text... there simply are too many variables beyond the scope of spreadsheet programs.