MEMS microphone gain calculation for MCU ADC
Well that calculation works fine for sine wave audio being measured by the microphone but real audio has a significant crest factor and this means that the peak voltages will be much greater for the same acoustic power signal. If you want to avoid distortion/clipping consider crest-factor: -



Picture from here.

You should also consider that your ADC will never be operating fully from rail to rail so assume 50 mV top and bottom of the 3.3 volt range is off-bounds. This is because of zero offset and gain errors.