Add Song to Automix Queue

I am using an iPad 2. For whatever reason I am unable to figure out how to add a song to my Automix Queue. Sometimes after I hit the “+” the song shows up in the list, most times it does not. Any clue as to what I am doing wrong?

Wow I really feel a bit dense. Thank you for taking the time to respond. You solved my algoriddim issue. Not sure what to do about my “density” issue. Cheers. Dave

You must hit the dune butten at the top when finished