Has Allah forgiven me for my promise to abandon sin after I fell into it, regretted it, and repented, and will I be punished by falling [into sin] because of that?

Your covenant with Allah Almighty is equivalent to an oath and a vow. If you violated it and were unable to feed [the needy] and fasted, then you have fulfilled what is required of you. As for supplicating against yourself, it is not befitting. Rather, you should supplicate for yourself with good, while having a good opinion of Allah and performing sincere repentance. If your repentance is true, Allah will forgive you and pardon you. We ask Allah that that supplication does not harm you.