Point to / show us where you want the fill to happen. The blue lines are not a closed shape, they are just two lines that do not connect to any other lines.
Duplicate the upper and lower red lines and place the dupes on the blue layer, then close these new dupes with the original blue lines to create a closed shape for the top and bottom of this design.
I have visualized what @ Rick has explained.
Remember, everything that needs to be filled must be a closed shape.
(I achieved this very easily by tracing your original drawing and deleting the non relevant lines)