How do you re burn on a CD-R?

You can't. CD-R is a read-only medium.

Some software will allow you to create a multi-session disk. This is generally only used for data discs though, not for music. With a multi-session disk you can burn multiple times, but you cannot write over any existing data. So, you still only get a total 700MB of data, but you don't have to write it all at once.