Video Walk-thru Using Copyright.gov
Go to https://copyright.gov ... "Register" works... Log in - register new work.. and use a form SR to copyright your song and say you've included other copyrighted material. In this case, the song is treated separately from the instrumental, and you have a license to use the included copyrighted material (our beats) if you've purchased / leased rights.
Form PA can be used as well, protecting you from others re-recording and publishing your song. For the most accurate legal advice concerning copyrights, contact an entertainment attorney.