its fine it sounds like it was just friction and not only that but you do swell not only when you have sex but alot when you orgasim... its probably just how your muscles are right now... give it time and a nice hot bath might hurt at first but dont use scented soap down there... just soak in the hot water then if you want take a shower to get soapy
I can't SEE what you describe so it's not safe to guess. If it's not less swollen by the morning or is really painful, see a MD. IF you had some rough sex, it might be trauma from that, but you didn't mention anything like that.