The dedicated GPU you chose will only show up in About this Mac when it's being used. It uses a great deal of system resources which is necessary for rendering video, playing games and various other graphical intensive applications, which cause heat and faster battery drain. If you need to make sure it's there just go into System Preferences and choose Energy Saver. Uncheck the box that says Automatic Graphics Switching. Then go back into About this Mac. You will see your dGPU.
I would highly recommend that you go back and re-check Automatic Graphics Switching or the dGPU will remain on at all times and you will notice fast battery drain.
Another thing. Some apps that don't seem like they would activate the dGPU will such as Chrome, will. If you must, only use Chrome when absolutely necessary because it activates the dGPU and will drain your battery and use cause high CPU usage.