Sending a big band score to someone who needs a score for his band?

Is there a way to send a big band score to the leader of a big band that wants to hear my score to use in his band?
He said I should send away to Washington DC for a copyright for the song, or send a letter to myself to protect myself from having it stolen by someone. Doesn't MuseScore have some type of copyright system that protects your original score?
Thanks for any advice!