Look, I agree with Milosuperspesh. It's got potential, but you need to work on character development, story development, the pacing of the story, all of that. Also, your characters aren't very likable and are a little confusing. You made it sound like James is a big pedophile by saying that she looks really young and would be hot once she filled out. Also, why would a girl that self sufficient not know how to drive? Even if she's 15 and too young to drive legally, if she was going across the country robbing places, she probably would know how to hot wire a car. Why would she be hitchhiking in the first place?
And I do NOT mean it disrespectfully. I would love to hear the whys that you've left out of the story. Maybe give more specifics, too.
I don't know how old you are, or even if you're a man or woman, but if you saw some kid hitch hiking, would you be fantasizing about screwing them, or would you be wondering the fundamental who/what/when/where/whys? Who is she? What is she doing out here? How long as she been alone? Where did she come from? Why is she here? And, if you did start to think that she might have a sketchy past, would you really keep her in the car with you? If I thought she might be or bring trouble, I would have dropped her ass off just as soon as the thought hit me. And that would have been a great reveal for her true character.
James asks her to get out and she pulls the gun on him and tells him to keep driving. Brilliant!
The only way you'll get better is practice, so don't give up. Just don't be so close minded about critique, either. Smart comments aside, Milo gave you great advice. I wish I could get him/her to critique my stories.