How do you this?
(Better to make the 3/4" wall a singular closed 2D entity, and give it a Brush pattern, if one requires zoomed-up-real-close exactness.)
There are a few methods. Try this one and see if you like it:
>Activate the Polyline Tool
>Using Vertex Snap, trace over the walls entity you currently have, using Arc Segment (Local Menu) for the two arcs, and making sure to invoke the "Close" command (Local Menu) at the end.
>The arcs will be way out of whack. Activate the Edit (node) Tool and edit those arc radius green nodes, Nearest_on_Graphic Snapping to the pre-existing arcs.
>Apply the Brush pattern and scale you wish, to the closed Polyline.
What version of TurboCAD are you working in currently? In case we want to provide you and example.