A real quick way is to mai

A real quick way is to mail a copy of the music to yourself and DON’T open it when you get it back. The postal system will stamp the date on it. If the envelop is not opened, the contents existed on the stamped date. Safe guard it in case you need to go to court.

The proper way would be to contact the copyright office for the appropriate forms. Sorry, I don’t know the address.