Is it obligatory to pay out the remaining amount of the vow that my father paid and then returned to me, knowing that the full amount had already been paid out?

You were obligated to fulfill the vow from the first salary, as you vowed, because fulfilling a vow in the manner it was undertaken is obligatory if possible. Since the vow has been completely fulfilled, nothing else is required of you, but you should seek forgiveness for your shortcomings.