Sitting in an exam hall is the whole scene here, and the poem makes you feel how slow it is. The opening lines are all small sounds: pens scratching, pages turning. In a silent room, those noises seem huge. The speaker is trapped in that quiet, and the question "When will it be over" comes back again and again, with "over" repeated twice more each time, like a clock ticking or a wish said under the breath.
Between those refrains, the thoughts wander. One moment the speaker is warning themselves to keep their head down and puzzling over a question. The next, they drift into remembering "long lost / People, things, lives," which suggests the mind escaping the pressure, perhaps into sadness or nostalgia. The poem doesn't explain who or what is being remembered, so it stays mysterious.
The mood is tense, restless and a little weary. The ending, "Pens down," is a relief, but the word "'till" hints the freedom is only temporary.