The expiration date on your copyrighted music isn't something you have to worry about, at least not in your lifetime. The music that you've written is copyrighted the moment you've put it onto paper or recorded it. The reason you don't have to worry about expiration is because the music is protected until 70 years after the death of the author. In the case of your music, that author would be you.

This rule about copyright music expiration was first put into place so that the families and heirs of an author could still earn royalties even after his or her death. Ultimately this means that if you've taken the steps to copyright your music and have registered the copyright, then your music will be protected throughout your lifetime until 70 years after you or the last surviving author (assuming a collaboration) is deceased.

Copyright music expiration is not something you should make a primary concern unless you are having issues of someone respecting and/or honoring your copyright at the moment. You should take comfort in the fact that as long as you are alive you are the only one who can assign your copyright to another person; and as long as you haven't given up your ownership of the music it still belongs to you.

This is different, however, if your copyrighted music was work made for hire. If that is the case then you cannot have ownership of the music, as it never legally belonged to you, but the person or entity who hired you to produce the music. Works made for hire have different copyright music expiration than those owned by the creator. With works made for hire, the copyrights are in effect for 95 years from the original publication date or for 120 years from the creation of the work, whichever of the two is shorter.