How do I get the PIR sensor to output more than 3.3v?
The PIR sensor output is a signal.  It is not intended to drive LEDs directly.  Fortunately we have such things as transistors that can switch LEDs on and off in response to a signal like what the PIR sensor puts out.

This simplest is to use a N channel MOSFET as a low side switch.  At the low voltage of 12 V, these are available that can be turned on/off quite nicely from either 0 V or 3.3 V.  The IRLML2502 is one example.

Drive the gate of the transistor directly from the 0-3.3 V digital output, the source to ground, and the LED string goes between the drain and the 12 V supply.