Based on the answers provided, the following corrections need to be made to the 3D object:

1. Add a second square-shaped cutout at one of the corners of the rectangle. This will ensure that the object has two square-shaped cutouts at two corners, as required.

2. Ensure that both square cutouts are located at the corners corresponding to the longer edge of the rectangle. This will correct the current issue where the existing cutout is not located at any corner of the rectangle.

3. Make the edges of the square cutouts rounded. This will clarify the shape of the cutouts, which is currently unclear. 

By making these corrections, the 3D object should meet all the specified requirements.