mistake during mounting a .iso file

I wanted to mount an iso file,so i used this command

sudo mount -t iso9660 -o ro,loop /path/to/file/dvd.iso /path/to/mountpoint/

but i did a mistake and instead of using an empty folder as destination i used an already existing folder,which had important folders inside....
Now it's previous content is gone and the file is locked. I can't change it's settings because it says that i am not the owner and i can't change the settings...

Can anyone help me?

Is the previous content gone forever?