Quick question about backup and disk format

in windows 7, I have no external HD so created a backup and saved it to a 8.5 GB DVD-R. Maybe I was naive thinking that windows backup would automatically format the disk as the live file system, but now have ended up with nearly 7 GB of wasted disk space. I have only 1 good sized disk left (and little cash) so here is my question.

Can I 'copy' backup files to a fresh correctly formatted disk, or does it need to be ISO file ,will this create the same problem?

Have you tested this disk with windows restore?

I am sure the disk will work fine, my problem is that I cannot update my backkup, and I didn't really want to go through first back up process again.

What do you mean; do you need to put files into an iso to back them up? Not really...putting them on a separate drive saves them in case your primary drive fails no?
Make sure your using a decently trustworthy backup drive in accordance with how important your data is, hopefully not some USB flash drive.

"Go through"? One click, walk away is too much to maybe save your data?
You're not doing it right.

Cheers for the constructive help.
Was just looking for a quicker solution to my mistake of incorrectly formatting dvd. My aim is to create a backup disk which can be added too rather than collecting a pile of backups, and cant understand why windows 7 backup would create a mastered disk for this purpose.
Either way will back up again on new disk, lesson learned.

Never trust a DVD-RW.
DVDs are cheap, or just get an external drive..