Yep, I bet that under your render dimensions you have the wrong settings, I'm betting they are 10 X 10.  If you like the setting in  Pose room, only larger you can enlarge your renderings proportions eg if your Pose room setting is 640 X 320, you can increase the final to 1024 X 768 etc.  Rendering to .jpg is fine if you set the rendering to 100 percent, you can't tell the loss unless you really enlarge the image 10 etc times.  If you have a 2D program like PaintShop Pro, Photo Shop elements, Photo Shop, Painter etc. you should export as a .tiff or .png like TG recommends because both contain an animal called an Alpha channel.  This animal is used to make the background invisible in your 2D program (look for mask, the alpha channel will appear there as a white image on a blackground, clicking it will make the background invisible.

Why would you want to do that, because then in your base layer, you can place a nice scene there with your image in the second layer.  Jan