Is there a repentance, and is this considered an oath or just a supplication, after I cursed my mother then regretted it, apologized to her, and she forgave me?

Quarreling with one's mother, raising one's voice at her, and invoking curses upon her are acts of disobedience (Uqooq al-Walidayn), which are considered among the greatest major sins and most heinous transgressions. One who repents from a sin is like one who has no sin, provided they feel remorse and their mother forgives them.

As for the statement, "By Allah, you will not see good," intended as a curse, it is not a binding oath (Yamin Mun'aqidah); rather, it is closer to presuming to know Allah's will (Al-Ta'alli 'ala Allah), which is impermissible.

It is obligatory to guard one's tongue, repent to Allah, and draw closer to Him through supererogatory acts of worship (Nawafil) and good deeds.