Have you read all the tutorial parts thoroughly? Have you finished the full tutorial? If not, make sure to do that first.
It is explained quite clearly that the number of parts and the size of the picture are intrinsically linked. Therefore, the first thing you will need to do is create a new set of blank shapes, the number of parts matching what you require. Then arrange them in the same way as part 2 explains, taking note of sizes etc. Part 3 covers the tile sizes.
It would make helping you easier if you posted your .capx.