How can fix music to have it play as long as the pictures in Windows Movie Maker?

I "added music" to pictures I assembled in  Windows Movie Maker and even though I selected the "Fit To Music" option in the "Project Tab", the music (green bar) doesn't carry throughout the entire movie of about 70 pictures?   Should I try to remove the music and re-add it again ?  If that is the correct action , I can't figure out how to remove the music and re-add it.  For clarification I did not import videos, I am only working with pictures and music.  I greatly appreciate anyone's advice on this! Thank you!