Hello, my dear. ♥ I'm here to return our swap.
Your grasp of the English language is amazing, so I hope you'll forgive me if I push you a little further. (I know that this is all stuff you may well have improved upon since writing this chapter, so I'll be brief.)
There were a lot of points where you included dialogue tags or descriptions that I didn't really think were necessary, and actually impeded the flow of the chapter a little. I also think that you should be careful about overusing qualifiers - things like "a moment" and "little" aren't always necessary.
For example, your first line would have sounded a little tighter if it had read, Fred Weasley threw himself on my couch. "So, what's the plan for Friday?" rather than "So, what's the plan for Friday?" Fred Weasley asked as he threw himself on my couch. It's a subtle difference, but it does make the writing come across as more polished.
Similarly, a little further down, rather than have "I had a fight with Jen," he revealed and a small frown appeared on his face for a moment. You don't really need the dialogue tag he revealed - it's clear that it's Fred speaking, and you typically use dialogue tags when either it isn't clear who's speaking or there's something distinctive about how they're speaking. This isn't really either. Instead, I think A small frown appeared on his face. "I had a fight with Jen." would have felt a little more polished.
Again, it's not a huge deal - your writing is perfectly lovely as it is. I just think that there are a few little things you could improve upon here and there to make it amazing. :)
Anyway. Onto the actual content. :P
I definitely believe Gwen's unrequited (?) feelings toward James, and I think you've played the best-friend-in-love thing perfectly, and in a way that's in keeping with the character you established Gwen to be. I could really feel how hurt and upset she was when their friends decided that they wanted a party and James went along with it, and I thought that keeping it in and pretending she wasn't bothered made sense. You don't want to force someone to spend time with you, you want them to want to.
I also like that she did end up blowing him off in the end, even if she felt guilty about it - unrequited love doesn't need to mean that she becomes a complete doormat, and I'm glad that you seen to be avoiding that pitfall.
I think that my major issue thus far is that I like Gwen a lot, but I don't really like James. I'm not quite sure what it is, since I tend to like the overconfident devil-may-care characters, but there's something about James that isn't clicking for me. I don't know, maybe it's just that right now, James is coming across as a bit selfish and thoughtless without a lot of redeeming characteristics. I don't dislike him, I just don't really see what Gwen does in him, and I'm kind of rooting for her to find someone else and get over James rather than for them to get together, if that makes sense. I just don't feel like he deserves her.
That said, this is still in the early part of the story, and it's entirely possible that James will end up becoming far more likable as it progresses. This was not a chapter that I think he was supposed to really shine in.
All in all, this was a really good chapter, and I'm definitely going to have to find the time to r&r more of it! ♥