I saw a video if a man, who was saying that Imam Hussein (PBUH) was useless, (walizoubillah), and I was about to curse him, then I stopped. Then I said Peace and Blessing upon The Prophet and His Progeny and Hasten Their Reappearance and Curse Their Enemies. And I may or may not have had the intention of cursing him when I said “Curse Their Enemies”.

Did I commit something wrong?

Do I have to reach out to this person and apologize?

In this case you should curse this person. Saying Imam Hussain (a) is useless is a major sin, and it is disrespectful to Allah and the Ahlulbayt. Such a person deserves to be cursed. Do not hesitate to curse him.