Since you are uploading a music file that is probably at least a couple of megabytes in size, it is going to take awhile for the upload to complete. Even over a typical 'broadband' connection, it can take a few minutes.
Please be patient and let the upload complete (don't navigate away from this page) - you will be sent to a confirmation page once the upload completes. AND you will also be sent a confirmation e-mail with a link to the song for you to double check.