Well, husband and I brought the tree trunk inside in order to let the polyurethane dry more completely and we made a happy discovery: after all the effort to level the tree trunk, we discovered that by swiveling the wheels, we could affect the height of the lowest point on the trunk enough so as to level out the top surface.
I took a cup of coffee and placed it on the top and it's level enough to place a container with liquids inside and not have it spill or tip over. Here's a photo:
That was a happy discovery.
Next, I'm going to go and purchase some concrete patch materials later today and fill that hole you see in the center of the trunk and then press in some small stones for a decorative effect. More on that later on.