Welcome to Android Central! Where did you get the tablet from? Was it brand new or refurbished/used?
Go through the System Settings and look for anything like Demo Mode. Also go through Settings>Apps>All and look for a Demo Mode app there. If you find one, Disable or Uninstall it.
If you can't find anything like that, then you probably were sold a floor model that has a demo mode ROM installed. You'd have to flash the original stock firmware on it to get rid of the demo ROM (I'm not sure how easy this might be). The easiest thing would be to return or exchange the device.