I'm having trouble copying already backed up DC backups using Nero 5

[killa_007]

I'm having trouble copying already backed up DC backups using Nero 5. For example if a DC game is 650 megs and when i ####t the CD copy option in Nero and the image that it's reading go up and over 700 megs sometimes even to 800 megs. i am reading at 2x and writing at 2x and i am copying the image on to my hard drive first..........please help.