I'm trying to use 3v LEDs in a 12V circuit, in my car
By decoding your question, this is what I arrive at: 

You are using the two resistors as a voltage divider, with the LEDs wired in parallel connected to the junction of these two resistors.  







simulate this circuit &ndash; Schematic created using CircuitLab

This is not a valid approach, the voltage divider will not provide the 1:4 (approximately) voltage division your calculations indicate. 

Firstly, either apply the three LEDs in series, with one resistor in series, or if you must have them in parallel, each will need a series resistor.  







simulate this circuit

The above indicative values of resistors are assuming 20 mA per LED as optimal. Do your own calculations for your specific LEDs.

For a ready to use online calculator, use an "LED resistance calculator" instead of a voltage divider one. This one even provides the correct schematic or wiring diagram as you prefer, to wire the LEDs up.