1- Select your music in GarageBand and send it to yourself.
2- Once received, click once on the attachment in your email to download the whole file. Once completed, click and hold to "Open with..."
3- Simply choose Cute CUT. It will then open and tell your that the file is now in the "iTunes" folder. You can now import your music simply by selecting a music source from the shared "iTunes" folder.
See the result: