I have backed up a database I had created on an other machine running SQL server 2012 express edition and I wanted to restore it on my machine, which is running the same. I
Sandra Walter's Answer provides an accurate description of what has happened, but I found the answer a bit lacking.
To make a backup which isn't striped (which is what has occurred in this situation), go back to the window where you setup the backup of your database. At the bottom is a list of paths where the different stripes will go to.
Go to each of the listed paths and delete the stripe of the backup.
Then remove all but one of the paths from the list in the window. And click the "OK" button. Your unstriped backup will be created at that one path.
Hope that helps.