App in Bluestacks help

Ive been using Justin App on a PC under Bluestacks --Been fine for months but now when I open it has been resized to a pillarbox style .Bluestacks window is still full screen but cant for the life of me get the app resized to full screen again.
Anyone have an answer ?

Ok got a response from Musopia–no longer supporting/optimised for Bluestacks. Back to the iPad then.