I have never had a problem fitting Kubuntu onto a standard 700 MB CD blank.
The only difference is that I have used K3B, the Kubuntu disc burning
software. In this app there is a menu item to allow over burning, which
should not be necessary, but one never knows...

If all else fails, burn it to a DVD blank. Unless you havea hardware
problem it will work.

You can try K3B easily as it's in the normal repositories. Don't give up on
Kubuntu too soon! There is no good reason why you can't burn a usable disc
and install it properly.