Cleaning Up A Shape

I have this shape (made ito a componet). It was a square, for which I rounded the corners using the arc tool.
When I pull and push, the block has the vertical lines where the arc ends are. How do I get rid of them? If I erase the lines, I lose the face.

I want to be able to apply the offset tool to the shape. When I do this now, the interior of the offset doesn’t have the matching rounded corners.

You can Weld those edges before Pushpull and you won’t get those edges, or you can use the soften smooth tool.
As to the offset, it will start as a curve but after a certain point it cannot be a curve and will become a corner.