You said this is your first story for Literotica. I'm going to assume iut's your first attempt at fiction as well. Welcome to the world of fiction-writing, with all its joys and travails.
Fisrt of all, it's good to see that your spelling and pinctuation are good, so you don't have to worry about trivial but essential stuff like that. You have a noticable propensity to use--what are they called? participial phrases?--that sentence construction that goes "Having started a story, I'll write it like this." In fact your first paragraph consists of nothing but sentences of this type, and it grates on the ear quickly. You need to add soem variety to your sentence construction.
Your bigger problems though, in my view, are ones that fiction writers have always styruggled with, such as how to tell a story, how much to tell, how to incorporate the characters' background into the narrative, and how to make the story some alive and seem real. This is where writing becomes an art.
Yes this idea has been done many, many times on lit, but in fact there are very few ideas that haven't been done on lit, and just because it's been done before doesn't mean you shouldn't tell your version. The idea and plot is only one ingredient in a story. And when a young hitchhiking girl gets into a truck with a man, we all know immediately what's going to happen. At least, on Literotica we do.
There is a distancedand flatness in your narrative tone that comes from your avoidance of describing the direct action. By that I mean that you;ll tell us, say, that she's out hitchhiking but you don't show us her standing on the side of the highway with the widn blowing her hair around, hugging herself against the cold, nervously sshifting from foot to foot, things like that. You'll tell us that he's driving alone thinking how happy he is becauyse he's 35, divorced, and has a job (would anyone really think something like that? Do you ever think, "Buy , am I happy!"?), but how about instead syou show us him sitting back with his arm out the window, singing along to the radio, maybe thinking about what he's going to do ay the end of the run when he gets paid? From that we'd get a pretty good idea that he's happy.
This is what we call "showing, not telling" and it's another part of the art. How do you show what characters are thinking without prying into their brains? By what you show them doing and by how you describe them doing it. Is Ashley hiding behind her suitcase awkwardly putting her thumb outr every so often, or is she standing with one foot in the lane of traffic and sticking her chest ourt to attract attention? Tell us which and we get a good idea of what kind of girl she is. Does he slam on the brakes as soon as he sees her or does he doubt what he sees or does he keep checking her out in the rear view before pulling over?
The nexty point is the believability of the characters and the situation. All of the stories here are pretty much fantasy to a greater or lesser degree, but the most exciting stories are the ones that seem the most real or plausible.
In the world I know an 18 year old attractive female would not be hitchhiking in a see-through tanktop and skirt unless she were going out specifically to get laid or cause a car crash. She probably wouldn't be so perky and upbeat climbing into the cab of a truck with a man she's never seen before dressed like that, and I doubt he would be reminiscing about his good old days on the road once she did. At the very least he would be struck by his good fortune, and he would immediately start thinking sexual thoughts, no matter how much of a gentrleman he was.
She appears to be running away from something. Girls just don't go out hitching like that so they can see the world. If she's running she would tend to be somewhat secretive or self-absorbed and not so naively open with herself. It just isn't believable.
Also, you don't have to [aint such a detailed description of her. This is always tempting to do, but it's an amateur's pitfall. If you have to describe her, you describe her through her actions, as she, say, "brushes her long blond hair out of her face", things like that. Characters don't like to sit still and pose for their portraits.
One of the prime laws in fiction is "write what you know". If you don't know what it would be like to be Ashley and can't imagine it well enough to make it seem real, find another subject. But it shouldn't be hard to put yourself in her place and really think hard through what her emotions and actions would be, how you would dress if you were going out to hitch hike, what you would take (would you really put your money in your suitcase or would you keep it in your mposket--or better yet, your shoe. Just what kind of toiletries are you going to take? Bath gel? Cream rinse? perfume?)
And one thing made me laugh. When she's watching him get gas and admiring him she thinks to herself that he looks like he could bench press a lot. I didn't know that this was something women looked for in a man. Doesn't she care about how much he can french curl or dead lift?
Just kidding. But the problems you have are the problems we all have and we all struggle with. I'd suggest you start reading--and not just the stuff here, but good stories by good short story writers--and pay attention to how they handle these problems. How the bring their characetrs to life, make the story believeable, tell the story, things like that.
For all that you've made a good beginning. Just don't stop now.