Final answer:
The author explains her excitement about the ocean before revealing her terrifying experience to show the contrast between her initial expectations and the reality.
Step-by-step explanation:
The author explains her excitement about the ocean before revealing her experience in paragraph 3 to describe how her panicked experience is different than her initial joyous anticipation. By first highlighting her excitement, the author creates a contrast between her initial expectations and the reality of her experience, which ultimately turns out to be terrifying. This contrast helps to emphasize the impact and significance of her later negative experience.