Must I perform two rak'ahs every morning, in addition to Fajr prayer, based on a vow whose wording I am not certain of?

If the intention was to make up for a missed obligatory Fajr prayer, this constitutes a vow concerning an obligation, and a vow concerning an obligation is not binding according to the majority of scholars. However, if the intention was to pray two supererogatory rak'ahs upon waking up, this is a binding vow that must be fulfilled. The general principle when in doubt is that a vow is not binding, so the questioner is not obligated to anything unless she is certain that she vowed to pray two supererogatory rak'ahs every time she woke up.