To eliminate white lines that appeared between my own picture and the rough shadow I created two shadows using a low flow and low opacity brush. I drew one on the underneath my image and one on top, reducing the white lines that were visible between my picture and the background.

IMPROVEMENT

 After some improvement to the image with the help of my teacher my picture started to look more integrated by copying my image again and changing the mode to Luminosity on one of the images and played with the opacity.

Another way to create a shadow effect is to use a radial blur that creates rays of colour and blends them into the image.

To be able to change the filter later on you need to first convert it into  SMART FILTER and later you may adjust the intensity and length of the rays.