I feel like baking! Chocolate sheet cake

I have never made this before, but I have tasted quite a few peoples variations over the years at parties & holidays. My Grandma gave me this cookbook from her church's fundraiser a few years back, thought I might try this recipe & see how I do! 
Why can't I follow a recipe exact? Seems like there is always a reason I cannot follow what the directions say. I did not have buttermilk so I substituted 1% milk. It was all I had, other than almond milk, which that would have been nasty. I added a sprinkle of cinnamon to the cake part, & only used 1/4 cup of oil rather than the 1/2 they asked for. I felt guilty about the 2 sticks of butter, so decided less oil was a good thing! Then I realize I do not have a sheet pan they call for to bake it in. I just had my 9*13 trusty Pyrex glass baker. So mine yielded thicker pieces. (oh darn) 
It did not specify if you are to pour the boiled frosting on the hot cake? But that is what I did. It made the center of the cake collapse into a fudgey cookie dough-type consistency... & the edges crisped up almost like a crust. Overall it turned out very good, as you can see the remaining sections got taken off to hubbys workplace so the temptation is out of the house!