You can try looking in System Settings> Window Behavior> Window Rules that is if you have that in your Applications Menu.
You can try this but I can't guarantee it will work.
Press ALT+F3 and go to: Advanced - Special Application Settings - Geometry
If that doesn't work the only other thing I can think of is to try holding down Ctrl & +
at the same time.
If not Rhythmbox for MP3 might be another alternative to consider.