Indicating 3V3 and 5V with 2 LEDs
First, using the gate voltage of a 2N7002 as a voltage reference is not a good idea.

A TL431 could be used since it has a nicely defined threshold of 2.5 V.  You can use two.  One is set to turn on at 3.3 V (taking all errors into account), and the other at 5 V.  You could use a lockout so that when the 5 V circuit triggers, it turns off power to the 3.3 V LED.