Hi there! I'll get to the point, im using 12 LEDS in parallel, supply voltage is 5V, forward voltage is 3 volts, and 20 Milliamps is the desired current. So, would a 3.9 resistor be too low if its all i have? or would it be okay if the circuit is on for long periods of time.

 

you need 100 ohms in series with each one or they will smoke.