That would provide a surface area of some 7,070,000 square microns.

According to this site, the upper-end of amoebic girth is some 30 microns diameter: Diameter of a Protozoan <hypertextbook.com>

Thus allowing the amorphous little bugger comfortable residence in an area of some 707 square microns.

That would get you about ten thousand amoebae on the head of a pin... something on that order of magnitude, anyway.

If I've miscalculated, I'm sure some SITO brainiac will let me know.