You need to open it up again and remove the metal shield. look at the bottom left you will see a black speaker unit with a blue and red wire. These are soldered onto the logic board. make sure they are not shorting with the metal plate in anyway and aslo that the solder joints are fine. This is your external speaker.
While you are also there. make sure you have aligned the front facing camera at top center of the board correctly. The other camera is at top right* near the little spring. make sure that is sitting properly in its seating.
Finally* if you also replaced the silver metal plate that was stuck onto the back of the digitizer* make sure you have lined it up properly with the transparent window in the digitizer.