I blame Bewitched, Charmed, and Harry Potter in part for this question. In all of those universes, Witches are born, not made. “Person has a mystical experience and discovers s/he’s got magical powers and is the only one who can save the world” is a tried-and-true theme of films, children’s books, and urban fantasy fiction. But it is exactly that—fiction. As in, “fun to read or watch but not true.”
We become Witches by choosing to become Witches. We either study on our own or with like-minded others or find a teacher who helps us. We declare ourselves to the god(s), or we are initiated into a circle or tradition by someone else who we asked to initiate us. The important thing here is that becoming Witches is our choice, not something we are destined to by birth or provenance. To me, Wicca and Witchcraft are pathways to self-empowerment, and the first step a Witch takes toward that empowerment is to choose to walk the path.
Now it’s possible you were born with certain talents or tendencies that lend themselves to Wicca or Witchcraft, such as the ability to sense energy, an affinity for nature and animals, or intuitive ability. But although it’s easy to interpret those things as harbingers of one’s impending Witchdom, they aren’t signs you’re destined to be a Witch. They’re signs that you’re sensitive to energy, like nature and animals, and/or are intuitive. No more, no less.
Another possible source for this question is the idea of reincarnation. Many—maybe even most—Witches believe that they have lived or will live multiple lives, although opinions vary on how that will actually happen and what it entails. One of the reasons Gerald Gardner, whose books popularized Wicca in the middle of the twentieth century, wrote about Wicca was that he wanted to be reborn into a Witch family in his next life. Personally, I don’t believe in reincarnation. But even if it’s true that a person lives multiple lives and was a Witch in at least one of them, it doesn’t mean he or she has to be a Witch in this one. Again, becoming a Witch is a choice we make, hopefully after having done our research, searching our souls, and maybe doing divination or asking the gods.
So if you want to be a Witch, go for it. But if you don’t want to be one, don’t be one, even if something or someone tries to tell you it’s your destiny. The choice is and always will be your own, and you should follow your gut and your heart in making it.