To tell you more about the procedure of the voice feminization surgery, you need to understand the vocal instrument, why you sound like you sound, and how surgery can affect your voice.
The sound source of your voice are your vocal folds. These will turn your air (power) into sound by vibrating. The vibrating frequency of the vocal folds will affect your pitch.
After the sound is produced, the sound will resonate into the pharynx, nasal structures and mouth. This will affect the timbre of your sound.