Creating atmosphere?

[Khyrpa]

You could try having new ambient sounds perhaps even a new soundtrack? Good example is White Night, it has a new soundtrack and that creates tension on first play. Those who have spent some time playing amnesia will find the original music almost comforting

Then you might test having cool lighting. Blue/Orange contrasts (...) or just torches that send shadows. A simple shadow can add a lot of depth to visuals. And visuals is one good way to create atmosphere.

Details everywhere... Your map doesn't seem to have any dim fogs, decals or details in general. More details give areas more personality that affects the atmosphere.

And spawning a monster right in the beginning of a story doesn't really give that much tension.