You can only get full 8 bit resolution of the duty cycle at certain spot frequencies. If you want any frequency then the range of duty cycle is limited.
Also you are best using pin 3 or 11 controlled by timer 2.
Without real numbers there is not much more I can add. Do a search for changing the PWM frequency, this involves poking values into some registers. The analogue write will control the width but it will only work up to a value determined by the main register.