I've never quite understood people having problems with cooking, honestly. When I cook, I'm always replacing ingredients, omitting things entirely, adding extra stuff (pancakes with corn in them are a personal favourite. Oh god yes) and it still comes out tasting good enough. In the vast majority of recipes, there is nothing so essential that the dish will come out horrendously if you ignore or replace it.
I think the "my cooking always comes out horribly" is either a consequence of doing meals that are overly complicated, or just being excessively fussy. Your cooking is not your mothers (or fathers, if you had a stay at home dad) cooking.