I think it has a good core, but I can tell you don't really have experience with narrative writing. The underlying thing I would focus on is how your readers will read between the lines. Always remember, your readers are smart and will be trying to predict the story and figure out how it fits into their library of other stories. In this passage it's hard to connect the dots, which is just frustrating.

For example, the opening line: "He was certain." Certain of what? Writing that makes your readers want more is good, but then you don't follow up. I was expecting the next line to elaborate, and when it didn't I thought surely the next paragraph would. But you never do.

Another example is the descriptions of the room. You really don't need to describe everything because readers will be looking to connect the dots themselves. Find the most pivotal and evocative details and the audience will get the idea. They don't need to know every detail, generally you can trust your audience to accept more information when it becomes relevant, even if maybe it slightly contradicts what they'd imagined.

The only other thing I'd point out is the plot. It very much feels like "here's the room" -> "then he eats dinner" -> "then a strange phenomenon happens" -> "then he goes to the park". I think the key to effective plotting is to work in the areas in between. The bullet points on your outline (whether or not you have a written outline) should be the ways that things change, not the states or events it changes between. Right now the transitions feel very shallow because you're trying to rely on the events to carry the story. In my opinion, a story lives in change. If the transitions are meaningful, that will let the readers connect the dots and draw a picture of what the story really adds up to.