Don't cut that cord and jerry-rig it. Use the correct cord for the ballast that you have. The cord is a "NEMA 6-15R", and yes that's American. It's used for equipment that need 240 volt @ 15 amps.
Many ballasts are multi voltage, accepting 120v/240v/277v/480v. It will be labeled on the ballast. If it will accept 120v, then just make it easy on yourself and get a different cord.
Hope that helps you out. I've been an electrician for 4 years now and try to help by answering electrical issues. Good luck.