All out of cake flour and all I have is AP and the recipe calls for 1 1/2 of cake flour and 1 1/2 of AP

I agree that using all AP flour should be fine, but you may want to triple sift it to incorporate more air, and be *very careful* not to "over-mix" batter after flour has been added.

This is an aside - one of the ways cake flour and AP flour are different is the micron size they are ground to. Also cake flour is "lower" in "protein." Cake flour is more thirsty/absorbent, so if I'm making flour substitutions, I always have extra "moisture" on hand. Moisture, in cake language is any of the following ingredients: sugar, butter, buttermilk, milk, eggs, egg whites, egg yolks. There are few cake recipes that balk at an extra egg, so use your baker's intuition when making the batter.

Cake flour will give a more delicate crumb to the cake, but AP is what most people have in their kitchen. It won't kill the cake if you use all AP.

Hi there! It's easy to make your own cake flour at home by sifting together all-purpose flour and cornstarch: https://food52.com/blog/8375-how-to-diy-cake-flour-and-self-rising-flour