If not already done so, let me suggest looking at my recent Tutorial Post and starting with a simple shape, loading it into Fritzing and add one or two simple parts and a Copper fill area.
Below shows the PCB from the Video tutorial with Copper fill added to the Top layer, just to confirm for your that it works.
Ensure you place the copper fill where it won’t cause problems - that may require some fussing - Fritzing is not perfect… thus, start with a clean test board, no cutouts…
