I'd don't see from the above where you made an image of the existing CD? You created a blank image. If you drag-and-drop into that image then the resulting CD will not be identical to the original.
You need to:
1) Insert the original CD (or DVD) into the drive
2) Start Disk Utility
3) Select the CD (or DVD) from the pane in the left. Select the top most item for the CD.
4) Go File->New->Disk Image from disk1... (note this is the last item in the New menu, it may be called something different on your system depending on the number of drives in the machine) if this option is not available select the next icon for the CD in the tree.
5) Call the image something sensible and choose DVD/CD Master as the format.
This will create a .cdr file you can burn (this is what I meant when I said create and image of the disc).
Burn that .cdr. If this still does not work then your CD may have some sort of copy protection on it to stop you taking backups. If that is the case you may need specialist software, or the publishers might replace your scratched CD for nominal cost.