Well there is no forced air. There isn't really any variables to have anyone look at. Short of sawing a hole in a wall, door or window.

According to this calculater:

• 400 ppm CO₂ in air would be about 0.72 g / m³
• 3000 ppm CO₂ in air would be about 5.40 g / m³

The room is about 20 m³ in volume. So in total that's 14.4 g to 108 g in a night. Ignoring any that diffuses under the door into the hallway, this would imply I breathe out 93.6 g of CO₂ in 8 h at rest.

A common number I see online for adult humans is 1kg per day. Makes sense that a significantly higher than proportional part of that is during waking hours, so I expect quit a bit less than 300g at night. Seems pretty plausible to me all-in-all.