The scans follow the wall detail so its not a perfect arc. My problem seems to be that when I go to create a boundary from my scanned points to create my part shape , cad does not like all the vertices and starts to do different weird things. I am assuming from all the vertices from the scan .

Then after trying multiple commands. I can get my boundary shape ,  but then the misc part , edit part will not convert the part to the shape .  The misc part just disappears . Again , I am assuming from all the vertices. I am obviously doing some thing wrong. 

In the attachment the back with multiple vertex is from the scan, the front is a CAD arc. I would like to create a Misc part from this .