My Rock Band Blitz soundtrack didn't download, or I only got three songs. How do I get the rest of them?

After you purchase and download Rock Band Blitz, you should immediately get a request to download the Rock Band Blitz soundtrack. If you don't get this request, or if you cancel it, you should get asked to download it again the next time you start playing Rock Band Blitz. If you don't get that, you should be able to restart the download from your account' purchase or download history.