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

1. Add a second rectangular hole to the object to make it symmetrical with the existing hole. The holes should have rounded corners.

2. Adjust the dimensions of the holes. Each hole's width should be about 5/12th the width of the object and the height of each hole should be about 7/10th the height of the object.

3. Ensure that the width of the object is twice its height. This may require adjusting the overall dimensions of the object or the holes. 

Please note that these corrections are based on visual assessment and may need to be fine-tuned upon actual measurement.