i think you might be seeing the barrel distortion of the lens. try standing back and zooming in, as this sort of distortion is more apparent at wide angle than telephoto. hope this helps. prob nothing wrong with your camera.

There are highly corrected lenses on the market, largely used by architectural photographers, that show neither barrel nor pincushion distortion. The lens alone would cost five to ten times the total cost of your camera - which may explain the distortion you are enjoying. Pretty much all zoom lenses exhibit barrel distortion at the wide end and pincushion at the telephoto end, including one I recently purchased that cost very close to $1,000. As jtj pointed out, by backing up and zooming in, through trial and error, you will be able to find a sweet-spot somewhere between wide and telephoto settings where it crosses over and is thus neutralized.

Perhaps a better solution and one that is immediate, is to fix it with your image processing program. Photoshop has a very elaborate distortion correction filter as one would expect, but inexpensive Paint Shop Pro also has filters that are highly effective and very easy to use. It also has easily learned, semi-automatic corrections for dynamic range, colour correction, saturation and the rest of the basics. If you have not yet invested in an image processing program, this is a good place to start. Adobe Elements is an excellent and highly affordable entry-level program that also has distortion elimination and many easy to use correction features. Both also facilitate manual processing as your skills improve.