All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
In principle, if one doubts whether or not he has performed an act of worship, then he has to perform it. This is because one is not acquitted from liability by doubt. If the liability is related to something certain, then this liability is not removed except with something certain. Al-Furooq authored by Al-Qaraafi reads:
“If a person is doubtful whether or not he has fasted, then he is obliged to fast. If he doubts whether or not he has paid the Zakat, then he is obliged to pay the Zakat.” [End of quote]
Based on this, if you are in doubt whether or not you had fasted the two days you vowed to fast, and you are certain that you have made a vow to fast them, then you must fast them now.
Allah knows best.