That would be the optimum mix, anything close will do.
You are applying 1lb of Nitrogen per 1000 sq ft
and just over half a pound of potash.
Additional potash will give your turf some drought resistance.
You probably do not need any additional phosphorus unless you are
bagging and removing your clippings. What was the soil pH?
Concentrate on getting the nitrogen right and keeping the phoshorus to
a minimum and you will do ok.
Remember on the fertilizer bags the numbers are percentages.
100 lbs of 20-3-12 contains 20lbs of N