After registering, please allow 2-3 business days for your account to be activated. Once active, you'll be able to start uploading and have full use of the My Score service.
Tip: You can set up your composer profile while you’re waiting for your account to activate. You can also use this time to learn how to properly upload your music by reading the following articles:

Publisher Profile

Before Uploading to My Score

Step-by-Step Guide to Uploading Music to My Score