Minecraft wiki entry for Recover_corrupted_saved_world_data, associated text: You will start in a random location and have to find your way back to your settlement.
You might start underground and suffocate. If this happens you will lose all your items again (the ones you put into your inventory in Creative mode in BlankWorld). If you want to keep your stuff, start the whole procedure from the top. After filling your inventory in BlankWorld, make sure to put a stack of ender pearls in the first slot. When you suffocate, try to escape by looking up and using the ender pearls. You can also try to put yourself at a higher altitude in BlankWorld. You may then die from fall damage, but your items will still be there after you respawn. Or, use the keep inventory cheat to make it easier. Although, you can turn this gamerule cheat off afterwards. If you find it too 'unnatural' for your Minecrafting standards.