can't mount a dmg image i made of my os drive

Hi there,

i was told to back up my HD at a apple care centre in France because they had to replace the mother board due to issues, i used disk utility app to create an image then planned to restore it, i did verify it and all but when i got the macbook pro back and tried to restore it again it got these errors saying ; unable to mount APPLE SSD SD256 media.dmg (no mountable file system), i really want to just get to my scrapbook folder in the user doc folder, its a firefox...

can't mount a dmg image i made of my os drive