Hi there, we went back into the extras.rpy file to check the behavior of the Music Room and the buttons are supposedly labeled correctly, according to the documentation.
hbox: # Buttons that let us advance through tracks. textbutton "Previous" action mr.Previous() alt "Previous Song" textbutton "Next" action mr.Next() alt "Next Song" null height 20
However, upon testing the template, it seems that your observations are correct: clicking on Next will cause Ren'Py to play the song listed above (or loop back to the bottom of the list). We'll notify PyTom about this bug unless it is intended behavior.
We also apologize if the template is difficult to adjust for 1280p. Have you tried using the Change/Update GUI button on the Launcher?