The speaker lists things they aren't: a ballerina, a star, a model. Each one stands for an ideal of beauty or success, and each comes with its own picture of perfection. The ballerina is "light on my toes and graceful," the star is "beautiful but out of reach," and the model is "stick-thin and perpetually smiling." The word "maybe" at the start of every line makes the tone gentle and a little unsure, as if the speaker is quietly testing out the idea of not measuring up rather than announcing it.
The turn comes in the final line: "But maybe I'm happy anyway." That "but" changes everything. After all the comparisons, the speaker lands on contentment, and the "maybe" suggests it's a hope they're still growing into rather than a loud victory. The mood is soft, honest, and hopeful. It doesn't pretend the pressure to look a certain way isn't there, but it shows the speaker choosing to be happy regardless.