All your curves look in a way similar and all look similar to the correct buffer capacity curve, I have no idea what you mean by a "perfect curve".
β definition you give is a little bit strange. (conc. Naoh*ml NaOH)/(1000*Total solution in litres) is just molarity of NaOH added to the acid after being diluted. Then you multiply it by DeltaVml - CV is number of moles, which would make sense, however, multiplying V of titrant by C of titrant diluted gives just some random number, unrelated to anything.