The poem is a small moment of awkwardness wrapped around a memory. The speaker recalls sitting close to someone, and compares the feeling to "the first time / ever on ship." That comparison works two ways: a ship moves underfoot, so you feel unsteady, and a first time at anything leaves you unsure of yourself. The title, "Wobbly," covers both.
The last lines are the most telling. The speaker says "I am come to not know / what to do with / my legs." The phrasing is slightly odd, almost formal, as if the speaker has arrived at confusion rather than simply fallen into it. Legs are something we never think about until closeness makes us self-conscious. Where do they go? Do they touch? Do they get in the way?
The mood is shy, tender, and a little comic. Nothing dramatic happens, but the broken, hesitant line breaks mimic the speaker's fumbling, and the feeling of being thrown off balance by someone's nearness comes through clearly.