Show Don't Tell
You have a good story to tell and that's what you did, tell the story in first person. If you are interested in becoming an author of thrillers or horror novels, you must "show" the scenes. Dialog, scene description and character development are important to readers. Show that your hero is happy by having him whistle as he works, or something that will illicit a feeling from your readers. Try your hand at third person writing which is the next step after learning first person.
Read the story now
Example: He moved through the horde of zombies whistling his good fortune of finding so many to kill in the shoe department. "Damn, this is gonna be a happy day." He pulled up his blood soaked bat and swung away.
I like your story, but to sell a story you must engage your readers with dialog, action and detailed scenes. The only reason I know this...is that I'm a bestselling author of medical thrillers, horror and suspense.
Cherie De Sues