A person has been lying around with a journal for days, and the poem is short enough to feel like a single exhale. The title, "Journalism," is a bit of a joke: it usually means reporting news to the public, but here the only audience is the speaker's own notebook. The "journal" is both a place to write and a kind of companion.
The middle image is the strangest and most vivid: "a hot sandwich / of security and regret." A sandwich is something pressed between two layers, and that seems to be how the speaker feels, comforted by staying put yet sorry about it at the same time. Being shut away is safe, but it also means time slipping by.
The final lines turn quiet and almost formal. "I confess my ruin" sounds dramatic, yet it happens in "evening quiet," so the mood is more tired honesty than panic. The poem feels private, a little wry, and gently sad, like writing down the truth only once nobody else is around.