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

1. Change the shape of the object from rectangular to square. This means all sides of the object should be of equal length. 

2. No changes are required in terms of the object's extrusion as it is already extruded in one dimension.

3. Ensure that the length of the object is not twice the width. Since the object should be square, the length and width should be equal.