This is pretty good. You have a firm grasp of your technicals; your biggest problem is that you have a habit of dropping commas, and even that is partially an artistic thing. The only real error I saw was that "Okay" should be spelled, well, like that, instead of "O.k.", which gets the point across but is more confusing.
Structurally, though, you could stand to have more confidence. The story is not about Sabrina and Jenna, is it? It's about Sabrina and Mr. Smith and whatever it is he's going to get up to with her. As such, what I want to read about is Sabrina and Mr. Smith, and whatever he's going to get up to with her. All this stuff with Jenna is irrelevant. Sure, it's hot, if you like that sort of thing, but there are
rare people (like myself) who don't care too much for girl-on-girl, and it doesn't advance the plot. It's sexiness for the sake of sexiness. Now, that in itself isn't a bad thing, especially given the publishing venue, but the problem is that you do it by sacrificing the story. You put the plot on hold for sex, and that is, simply put, the wrong thing to do in a story.
Here's the thing about sex stories: we only care if we already care about the characters. Right now, somewhere in this wide world, two strangers are having sex. Does that matter to you? It probably doesn't. Why? Because they're strangers. Their emotional and physical adventures are irrelevant to you. Stories are the same
. Your audience may be turned on (or not) by the thought of these two nubile girls writhing together in pleasure, but if there's no emotional connection they're not going to come back. And unfortunately, there isn't one. You haven't shown us much about Sabrina to make us care about her. Oh, she's an orphan, yeah... but that's kind of a cliché. Oh, she's so nice that even the tough girls respect her... But that's also kind of a cliché. Uh-oh, she's being put into a mysterious situation under a man with the most common last name in the English-speaking language! Now this
might not be a cliché... But you didn't tell us anything about it! You chose to describe three minutes of writhing instead! Aww man, and here I was hoping to find out who Sabrina really is
, not just the fact that she, like most teenagers, is horny. I want to know what makes Sabrina special
--what is going to show me that only she can; and, by extension, what you
, The Writer, are going to show me that only you can. And, when the first chapter ends without any sign of such uniqueness, I lose interest in the reading a second.
Now, before you get defensive, let me be clear: this is a problem that writers only have when they're good
. You would not believe how many people come through this website who haven't figured out what punctuation is for. Your problem, on the other hand, is in little things like importance of information. What are the things I absolutely
have to impart on The Reader to keep them interested? Without knowing the answer, you wrote a perfectly serviceable chapter that people like. You're already way
ahead of the curve. So keep writing. Things could be way worse.