I was in creative mode on minecraft PE. I made this really awesome house plus a hotel! I was finishing up my house but decided to explore first. I explored for about 10 minutes and then stopped. Suddenly, I started worrying because I didn't know where I was. I couldn't find my house on a map, a compass, and I didn't make a beacon or keep track of what side of the sun it was on either. How can I find my house again???
A 3rd party solution:
You could download a map viewer that loads a Minecraft save and renders the entirety of the world in a 2d layout. Then, remember a biome that was either close or home to where your mansion was (for example, was it in the taiga biome, desert biome, etc.), then look in that area.
Some map viewers allow you to scan a map for particular objects, like chests and other items. So since you made a flat grassy world, you would need to look for items like chests, wood stairs, the blocks you put in you mansion and you should be able to find it.