I'm making a color organ and each of the three panels has 100 leds on it.
Use THIS excellent tool to design a parallel-series LED array.
Except it is very bad form to wire LEDs in parallel because what happens is, due to minor manufacturing differences between the LEDs, one of them sinks all the current and the others won't light.Best to wire them in chains of about 10 with one current limiting resistor per chain and then parallel up ten of the chains. for each panel. You will need more volts but the chances of it working and all the LEDs roducing the same brightness are also higher.
What are the specifications on your LEDs? If they are all in parallel, then the voltage required is just the voltage for a single LED (draw the circuit to make that obvious to you). The current required is the total current for all of them (i.e., 300 times the current for a single one).