Is this occurring only while you're holding your phone in landscape mode or in portrait mode, or is in both?
It this only happens in landscape mode, it sounds like it's just 'stuck' in its portrait mode appearance. Could be just a one-off glitch so rebooting your phone might solve the problem. If after a restart the problem is still there, go into your Settings >> Apps menu, find the listing for your keyboard app and open it, find the 'Clear cache' button and tap it, then see if your keyboard is still not showing up properly.