Hi Peter,
It would be good to confirm which Operating System you are using. Is this Windows? If so, the window size when you run a COBOL program through the Eclipse IDE is controlled by the system settings for the "cmd.exe" executable, as this is used for executing character based programs.
Try this: While the application is running from the IDE (the character window is displayed) right click on the title bar, and choose Properties. Then, choose Layout tab, and change the Window Size so that the width is 120 columns. Finally, click OK to close the Properties dialog. The next time you run your program through the IDE, you should see the wider window.