Having trouble with PWM library

I want to set up 4 PWM outputs on Arduino mega 2560 running at 20kHz.

Google search reulted in link to PWM.h library. I downloaded this and followed instructions to set up as shown below. My results are:
Pin 3 = 20 kHz
Pin 9 = 5 kHz
Pin 10 = nothing
Pin 11 = nothing

#include <PWM.h>
int32_t frequency = 20000;

void setup(){
InitTimersSafe();
SetPinFrequencySafe(3,frequency);
SetPinFrequencySafe(9,frequency);
SetPinFrequencySafe(10,frequency);
SetPinFrequencySafe(11,frequency);

pwmWrite(3,128);
pwmWrite(9,128);
pwmWrite(10,128);
pwmWrite(11,128)
}

void loop(){

}