Hi,
Even if a lot of people say that they have the experience that it works on 3.3V...
function simply is not guaranteed
* it may refuse to work after time
* it may refuse to work at different temperatures
* one batch may work, the other batch not
And for sure your 3.3V power supply will have tolerance and drift, too.
*********
Most 3.3V microcontrollers will work up to 3.6V.
So the safe way (if yo don´t want to replace any part) to use a 3.55V (nominal) power supply.
Thus you have symmetric +/-50mV of margin. Not much, but a margin.
Many power supply have adjustable output voltage.
Klaus