Are you sure that the end of the screen is not also the end of the recording?
From what I know, if I import a song into Music Maker, the screen or arranger area stretches out to the length of the audio I import... example. If I have a song that is 6:42 then the display in Music Maker matches its screen to the entire song I imported.
If you recorded material, make sure the entire recording is there. Try playing back that recorded file in Windows Media Player. That way you can check to see if the recording is complete.
Also... What version of Music Maker are you referring to?
If you hit CTRL+8 your screen will show the entire arrangement. You can find this command and many more in the Zoom menu at the bottom right corner of the arranger.