121 is norm. The advertised space is always raw unformatted space and is a convention used evrywhere (Whats your desktop HD capacity? try to measure that too

).
As for the 0.68MB used, I reckon that is also some used by file tables or things like that. If you can't see any listing using explorer, it is fine. Still if you want to be sure, you can format the card and then you will have maximum space available.