Would I be sinful for being ill-mannered with my father, who became angry with me and cursed me, praying that I be sent to hell, then forgave me after I apologized and kissed his feet? And would his prayers against me have been answered?

Allah has commanded us to address parents with politeness and gentleness, and He has forbidden us from scolding them, as stated in His verse: {So do not say to them [even] 'uff' and do not repel them but speak to them a noble word. And lower to them the wing of humility out of mercy and say, 'My Lord, have mercy upon them as they brought me up [when I was] small.'} If you repent from your ill-treatment of your father and satisfy him, then repentance is accepted. And your father’s supplication against you while he is angry will not harm you because Allah does not answer such a supplication, out of kindness and mercy to His servants. It is obligatory for the father to avoid supplicating against his children and cursing them, because cursing a specific Muslim is forbidden. Our advice to the questioner is to strive in being dutiful to his parents and to struggle against the whisperings of Satan.