One baptism is enough—but it must be done with authority.

When missionaries invite people to be baptized, they’re often met with a question: “What if I’ve already been baptized? Doesn’t that count?”

Sections 20 and 22 of the Doctrine and Covenants, revealed just after the Church was officially organized, explain these two truths:

• Being baptized as a sign of repentance and devotion to the Savior is always a good thing (see Doctrine and Covenants 20:37). The Lord is pleased when His children try to serve Him according to the knowledge they have.
• But the priesthood—the authority to act in God’s name—is found only in The Church of Jesus Christ of Latter-day Saints. Being baptized in good faith as a member of another Christian church is a step in the right direction, but without priesthood authority from God, “although a man should be baptized an hundred times it availeth him nothing” (Doctrine and Covenants 22:2).

So the answer to the original question is essentially: “Yes, your prior baptism counts as a righteous, good thing that made your Heavenly Father happy. You did what was best based on what you knew at the time. But now you know more, and the Lord wants you to act on that new knowledge to show your commitment to Him.”