The speaker stands at the edge of a confession. The first half of the poem is full of "I could": I could say I love you, I could impress you, I could make you look up. These lines feel hopeful, even daydreamy, as if the speaker is picturing the moment going perfectly.
Then "But what if" stops everything. The speaker worries about two things: their own ego being too big, and the other person's trust being too small. Put together, they seem like a bad match, and the speaker imagines the love ending in "one steady fall." That image echoes the opening line, "I could fall now," so falling in love turns into falling apart.
The mood is nervous and uncertain, a mix of longing and fear. The short, plain lines make the hesitation feel real, like someone talking themselves out of a risk before they ever take it. The poem leaves us with the question unanswered.