Urgent! - Can't Edit Legally Bought Music in GB

Hi, I have legally bought a christmas music selection frm a "Royaty Free" website. I need to fade the musuc for an animation project I am working on. When I play the sone in iTunes it sounds fine with no preview, BUT, when I drag it into GarageBand it says "preview" every few seconds throughout the whole song. I understand GB probably adds this a protective measure so people can't mess with songs, but I legally bought this production music and so I should be able to edit it shouldn't I?

The project is due tomorrow so I am panicking. What can I do?