Acid blend is usually a blend of tartaric, malic & citric acids (50%, 30% & 20%). Adding citric alone would be like only adding a small part of what is called for, but adding more to compensate would make it even worse by throwing your titratable acidity even further out of balance. I would use the acid blend, it's not expensive & is readily available at any HBS; and it should give you the end product your recipe says it will. The more you deviate from a recipe, the less it's going to turn out like that recipe; but then sometimes that's a good thing, sometimes not. Hope you find this info useful, GF.