[Qgis-user] QGIS rendering round (circle) polygons as diamonds, and cannot find reason or cure

[Robert D. Bowers M.A.]

QGIS version 3.1.8
I have a shapefile I'm working with, showing the locations of a number 
of what are called "post molds" - evidence that a post was put in the 
ground there at one point.  I've drawn circles for each post mold, but 
they're all rendering (showing) as diamonds - squares rotated 45 
degrees.  Other shapes also are not rendering quite as smoothly as drawn 
(freehand).

I cannot figure out what is causing this (the wrong shape for the 
circles).  I can draw ellipses and they show up fine.  I'm really 
reluctant to try to redraw any of the existing ones - there are several.

The map itself covered an area of about 50 meters by 50 meters.  The 
circles are all in the 2-5 decimeter range (approximate).

Also, is it possible to re-size an existing polygon - for instance make 
an ellipse larger than the original?

Thanks!

Bob