hemanayal:
I was able to get close by doing two things:
1. In the 3D Window, select the corner frame and change from Generic to Invisible, this will eliminate the frame in 2D and 3D.
2. Select the Panels and change from Generic to CW Corner Panel. Then change this to One Butted Edge and play with the settings until the panels overlap at the corner.
You should modify your Signature of your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David