Keeping to your measurements is extremely important. Have you ever had a recipe go bad?
I have a friend who once tried to make a cake but decided to do it her way. She didn't follow the recipe given and added a little less of this and a little more of that. What she came out with was a weird tasting egg.
It says 1/2 cup of butter and you say no I like my cakes buttery so you go and add 1 cup, it says 2 cups of flour and you say no, I don't have flour but I have cornstarch and it looks like flour so I will add that instead. Well that is why your recipe is a disaster. You need to stick to the measurements given. Be creative, but stick to the guidelines.