After cutting the main object a black space is left on your image. Using the Clone tool you can fill in the gap by duplicating portions of your image.
Select background and click on Start Cloning
Press Control and click on portions of your image that you want to duplicate, and let go of the Control key.
Move your cursor over the black space and click on it.
Do the same steps until space is completely filled.
Adjust the Radius, Hardness, and Opacity especially with complex backgrounds