Add some CMC to the sugarpaste. Keep on adding the CMC gradually until you feel that the paste gets thick (you have to use quite a lot of pressure to knead it). The paste needs to be thick/firm so that the squares won't lose the shape.
All squares need to be the same thickness (if they are not the same thickness it will be visible and you won't get a neat finish). To get the same thickness of all squares I used spacers to roll out the paste.
To make 3 mm spacers I stuck two lollipop sticks (each 1.5 mm thick) together with double sided tape. Since the sticks are short you might have to reposition the spacers to roll out the whole piece of paste.
To avoid cutting out too many squares I suggest rolling out a few pieces of paste, sticking the squares on and making more later once you run out of them.
Leave the pieces of paste to dry for a few minutes (or longer, depending on the amount of CMC added). The paste can't be too stretchy (soft) because the squares will lose the shape.