Creepypasta movies have a bad reputation for a reason. I have to respectfully disagree with your point when it's made this broadly, though.
In the mid- to late-2000s, when people first started using "creepypasta" to describe a certain kind of horror story passed around online, the label had a fairly specific meaning. Creepypastas were typically short, almost always anonymous works of fiction posted to websites like 4chan (where they predominated on the site's /x/ paranormal board, usually accompanied by unrelated but disturbing image files) that could easily be copied, pasted, and shared by any user. They were a little like Internet urban legends, although their veneer of credibility was usually thinner thanks to...well, the nature of Internet culture, and it's hard to imagine how most of them could have been fleshed out into a full-length movie.
Since at least the 2010s, though, the definition of creepypasta has broadened greatly. Some long-form stories existed before, but now they're much more widespread, and quite a few have enough content to serve as at least the nexus of a much broader mythology. Some, far from reading like digital versions of traditional urban legends, are set in worlds very distinct from our own. Probably the majority have known ownership, too, rather than being faceless posts on an image board. In 2021, creepypasta is a massive, varied body of horror fiction self-published online.
When it comes down to it, I don't think creepypasta movies suck because of anything inherent to the format. I've you've ever seen Marble Hornets, an amateur production based off the "creepypasta" character Slenderman, it's interesting, disturbing, and sometimes beautiful in its emotional depth. The problem is really that most mainstream creepypasta films are quick cash grabs, usually trying to throw shlock at a younger audience who are perceived to be less discerning, and often failing to catch the crest of the wave of a character's popularity thanks to the long production times of Hollywood films.
Honestly, it's probably the photo that hooks people in more than the story. Without being disrespectful to the original author (who is, of course, anonymous and may be very young or someone whose first language isn't English; God knows, anything I wrote in Spanish would be a travesty against the language), the pasta itself really leaves a lot to be desired.
To be blunt, that isn't the best motivation if you're starting out and intend to present your work to others. It can be a good way to challenge yourself, especially if you already have years of experience with writing as a hobby and want to see what you can produce under a specific time constraint. Otherwise, it's generally better to spend time plotting out the story that you want to tell, then to take awhile to read over and edit it for grammar or spelling issues.
Other than problems with run-on sentences and wording, pacing and format are major issues here. It seems like you intended to tell this story through a combination of journal entries and more traditional narration, but there's not really any coherent logic to where one ends and the other begins. That can be tricky to pull off in the first place (it's usually better to stick with one or the other). That the ending would be told in the third person makes sense, but the beginning really should be told the same way as the rest of the narrative.
When it comes to pacing, there should be some sense of impending doom. The protagonist believes that the world is going to end. Readers need to feel what he feels at that possibility. If his entire life is going to be torn apart, he should describe that feeling of dread. If you believed that ICBMs were about to be launched toward your location, would you just talk about threats from the USSR in your journal, or would you describe the horrible fear that gripped you? The same holds true for his other actions. He's killing and eating people, desperate enough to do so even though they're rotting, but I get no sense of desperation reading this. Overall, there's an issue with telling rather than showing.
"I ate the corpses even though they'd gone bad"
Is a pretty weak line. To make it work, you'd have to let the reader feel that the person's mental state had degraded beforehand. They'd have to start out describing things in more depth, then gradually go downhill. Compare:
"The goddamn generator died four days ago. I was thinking I'd have at least a week or so of power to keep them stored down in the ice box. The best laid plans of hyenas and vultures, huh? Went in there to check on them this morning (I think? Fuck knows anymore), and the smell nearly knocked me on my ass. Still...Jesus, what's happening to me? I was salivating after I got done dry heaving. Took out my knife and carved a little from Jessica's thigh there on the spot. So hungry, oh my god. Had enough butane left in the lantern to get a fire going, so I at least cooked the long pork off that sow before I ate it. Hopefully I won't get sick, not like there's a doctor around. Well, except for her. Ha! You know, it was hard to eat them at first. Even when they were fresh. Goes down a lot easier when you're all skin and bone, yourself."
Probably not that great, but you get the idea. You feel how far down the narrator had to fall to be willing to eat rotting human flesh.
Definitely sit down and read over this. Try to make it a little more descriptive, rather than just saying the bare bones of what happened. Horror is usually in the details, not the events. Especially if the creepiness comes from imagining yourself in the protagonist's shoes, you have to give the reader at least an inch for them to run a mile with it.