This post is already taking well-deserved flak, but there are a few reasons that this doesn't make sense as an account he'd make up:
1. We already know plenty about what Chris's ideal "sex time" is like, and it's not this. Even if you assume someone else gave Chris input, there are details here that Chris would never allow in an idealized sex scenario, like the prostitute not letting him fingerbang her (would Chris ever imagine a sex partner denying him anything?) and his not really reaching climax. (Yes, he claims that she climaxed and praised him, but she's a professional. She knows how to flatter a client.) Chris is always bizarre, unrealistic, and extravagant in his lies; if he were lying about an event of this level of psychological magnitude to him, do you really believe he'd let it sound this mediocre?
2. Chris's cybersex and fantasies tend to involve some really porny sex act or weird scenario that he's currently fixated on, and this is a lot more pedestrian -- and, not coincidentally, the sort of thing a prostitute would guide an incompetent, awkward virgin towards going for. In Chris's fantasies, he's an expert lover with full control, but here he gets cowgirl because he clearly doesn't know what he's doing.
3. If someone helped him write this up, wouldn't they have said so here? Is there anyone in Chris's life who would coauthor a fake first-time story and not immediately report on it over here? You can't tell me Anna or Barb read this and gave Chris advice about how to write a believably sordid, unsatisfying paid sex encounter.