Re: Frequency Not stable
as the pwm changes , your frequency measurement appears increasing , otherwise, frequency need not change. how ever you need to ensure that the 12V supply to the chip s cleaner from the load related disturbances, by taking precautions. the R and C used for the osc should better be MFR and polypropylene (box type , instead of a simple disc cap, as disc caps are bad as frequency setting components.
Artwork plays a big role in stability. always use separate wires from battery to the chip and related components. let the battery have separate (thicker wires that feed the load side.
NEVER USE BREAD BOARDED DESIGNS FOR THIS.
Hope with these checks and mods , you can be able to stabilize your board / design