Get NBTedit, open up you level.dat folder in the worlds folder on .minecraft on %appdata% then scroll to the bottom of it and double click where it says "pos: 3 entries of type TagDouble". Those co-ords should be the ones that you last left off from to get banned from single player. Change the one that should look like some numbers and letter (e.g. T3+2D) or something like that to where you want to go. If it was the Y co-ord you changed then put it to something around 70 which is just above sea level. I came on here just to find how to solve the same problem that I had, I had worked hours on this world and couldn't afford to lose it. I changed that number and now its back to normal. Have fun! Btw, this is my first ever PlanetMinecraft post.
