16MB Memory Card Too small?

[Shonumi]

Dolphin creates an "empty" file with a fixed size (16777216 bytes). When you make a new one, it has little data in it, most of it's just 0xFF in hexadecimal. The file does not expand as you add games saves. Rather, Dolphin reads and writes binary data to it (at specific locations that correspond to whatever save data a game needs).

So yeah, just try a fresh memory card file and you should be fine.