I want to say a word on trusting the reader. An inevitable sign of growth in a new writer (and we all go through this arc) is in the area of trusting the reader. Newbies who haven't developed the discipline of trusting the reader tend to over-explain simple things in the action lines or they over-explain obvious reactions in characters or they indulge in on-the-nose dialogue to convey obvious emotions we all know that particular character is feeling. Over time, you'll learn that you only need to explain something once (or not even explain it at all) and then move on because you know very well that your readers are with you, will get it without needing your help, and will appreciate you more for trusting them and moving forward. An example of this might be, like on pg 62, you mentioned that the gang saw "an ocean of trees." Okay, great. But then you had to add, "Absolutely no sign of civilization, whatsoever." Yeah. We got that with "ocean of trees." Let's move on. Do you see what I mean? I also mentioned characters indulging in on-the-nose dialogue to convey obvious emotions we all know that particular character is feeling. This brings to mind the moment after Kevin sees [his best friend] Josh [kissing his girlfriend] Emily, and he's all pissed off and he later tells everyone off. Well, we've seen this a billion times before. We all know exactly what Kevin's thinking and feeling, and it's moments like these where a writer has to find ways to show us something totally unexpected from a character. What if he didn't tell them off? What if he embraced Josh? Why would he do something crazy like that? What if, when Emily kisses him, he doesn't push her away but pulls her in, and I don't know, has angry sex? You lower interest by having characters play out in ways that are totally expected and you make people more engaged when they do the opposite.
You should also consider multiple setups in one scene. I'm a believer in horizontal / vertical storytelling. I think a writer should work hard to give the audience a smooth, seamless, and efficient setup to the story. You establish many things in as few scenes as possible to quickly move us down that horizontal plane of storytelling. That is, until you get to those vertical moments, which is the reason we're all there to see that film and the time when the story could slow down or briefly stop. In an action movie, it's the action sequences. In a comedy, it's the big gut-busting moments. In a horror story, it's the suspenseful moments of horror. So when you finally get to those moments, like when the engineer transforms and you have Angie on her way to see him, that's when you should slow down, focus your creative energies in dragging out the suspense to excruciating levels. I recently posted a murder scene on my blog that was actually written by Alfred Hitchcock from an unproduced screenplay. One murder scene took up 12 pages. Mind you, it wasn't the greatest murder scene ever since Psycho but it was fascinating to analyze. It wasn't about getting a murder scene done quickly in order to move the plot forward. It was about the EXPERIENCE of the murder scene. It was about the characters and the question of "will he or won't he commit murder" dragged out to excruciating levels. That's what horror does. And I think almost all of your scary scenes, which were good, could have still been dragged out longer, could've been more intense to heighten the EXPERIENCE for the audience. It's not about volume of scares but quality of suspense.