Receiving the rewards for fasting on virtuous days

Q: I made a vow that if I commit a certain sin I will fast for 3 consecutive days. Unfortunately I fell in to this sin many times after so I have 27 fasts to keep. If I fast with the intention of these fasts on days that are virtuous to fast like the first 9 days of Zul HIjjah, 13 14 15 of each month will I receive the thawaab that comes with normally fasting on these days or will only my vow be carried out?