How to entirely burn all 700MB of a CD while data is smaller?
Create the disk image first..  As a sparseimage or a dmg, etc…  Just make sure it is the final size of your desired media…  (presets are available in the "New" panel.  
Mount it.. Put what you want on it…
Burn it.  If it's a 700MB image… It'll get burned on all 700 MB.


Peace.