Large font in one cell

I have a cell that wants to display numbers in a large font. Working with Numbers 5.1 on Macbook Air. Pasted a number into a cell and it appeared in very large font, changing the size of the cell. To make the cell the size it had been I had to reduce the font size to 7 from 11. very hard to read. Have deleted contents of cell, restarted numbers, looked for the unhide, all to no effect. This cell has instructions I can't access! Any suggestions?