I was given a latch hook kit and decided to try it.

The actual backing is 6 “grids” across & 9 grids long. The diagram showing pattern/colors has only 5 across & 7 long. Plus there are fewer squares in the backing grids than on the pattern.
What am I missing? Am I supposed to cut the back to size and how do I follow the pattern if it shows, for example, 8 black squares followed by 2 yellow within a grid when I only have 8 total in that same space on backing?

You can probably tell I’ve never done this before.