The poem is a confession that keeps getting stuck. The speaker starts with a single word, "If," and adds one word at a time: "If I told you how I really felt." Then the lines shrink back down, as if the nerve has run out, until only "If" is left. The title line, "Austin plz marry me," suggests the person being addressed, though the poem itself never explains who Austin is or what their relationship looks like.
The shape of the poem does most of the work. The lines grow like someone taking a breath, then fall apart. Even the stumbles, like "how I how" and the lowercase "i," feel like nervous speech. Only at the end does the speaker finally say it: "I'm in love with you." The mood is hopeful, anxious, and a bit playful. The speaker is scared, but also so full of feeling that the words finally spill out.