As we see well the lines are not aligned with the frame...
The technique is excellent to correction of distortions that perspective play... And not complicated!
Do a copy of the background in Photoshop. You obtain an identical photo into a layer. Select that layer as active and go to the menu "Edit" Go Select Transform and select distortion. You can "pull" any of the 4 corners of the photo and position it until you are satisfied...
As you have the good result... "Flatten" you image into the "Layers" menu and save it...
It bring so,e very little difference here...
It's a small detail!