The speaker takes a familiar saying, "you are what you eat," and treats it as a literal plan. If you want to be beautiful, the logic goes, then eat beautiful things. So they eat flowers. It's a childlike idea, simple and a little absurd, and it's delivered with complete sincerity.
What gives the line its weight is the wish underneath it. The speaker says outright that they want to be beautiful, which suggests they don't yet feel that they are. The trailing ellipsis leaves the thought hanging, as if there's more to say, or as if the speaker trails off in a moment of doubt or hope.
The mood is gentle, tender, and slightly sad. There's something sweet about the image of someone swallowing petals, but also something vulnerable in how far they'll go to feel worthy. The poem is brief, yet it captures a very human longing to become what we admire.