Please don't use caps lock as it is considered shouting and therefore rude.
You cannot save the excel document to disc as the disc has already been burnt and cannot be changed at all (if it is a cd-r or dvd-r). But it can be changed if it is a cd-rw or dvd-rw. You must however wipe the disc and re-burn everything to it again. In fact it's a lot easier to use a memory key.