If you use the 'correct' resistor for 3.2V then the 3.0V LEDs might receive much more than 20mA.
I think you are over stating the case. If a led with a nominal 3.2vdc Vc rating was actually 3.0 Vf then the
90 ohm resistor would limit the current to 22 ma, hardly a thing to be concerned about, right? There can be more then that much variation in the arduino boards Vcc voltage depending on the USB voltage allowance of 4.75 to 5.25 vdc standard.
Lefty