Based on the answers provided, here are the corrections needed for the 3D object:

1. Change the shape of the object to be "U"-shaped instead of a rectangular solid with a rectangular cutout. This will make the object's overall shape more akin to a "U" rather than a frame or a box with an open center.

2. Ensure that the smaller rectangle cutout in the middle of the larger rectangle is approximately 2/3rd the size of the larger side of the original rectangle. This will help to clarify the proportionate size of the smaller rectangle relative to the larger rectangle.

3. Modify the smaller rectangle so that it is connected to the top edge of the larger rectangle. Currently, the smaller rectangle is entirely surrounded by the material of the larger rectangle, indicating it is enclosed within the larger structure. This needs to be changed so that the smaller rectangle is connected to the top edge of the larger rectangle.