My Minecraft world is shrinking!

My world is shrinking! Plz help what do I do. I couldn't go out of the border (old style world) and I was in a boat at the edge of the border and i saved and quit and when I came back the next day where I was had disappeared! Everything in it was shaking uncontrollably and I couldn't move so I /killed myself and only respawned when closing and reopening Minecraft! The world is still getting smaller every time we reboot the Xbox!