Step 7 - Segments and piezo sensors
While the color on the case dries you can add the rest of the segments to the segment section.
You will need to separate the segemnt section from the matrix section to do that. So while you are already in you can as well just stick the piezo sensors with a bit of sticky tape to the segment section and let the electronics hang from the side like pictured below.
Case is dry now? Well then you can fit the electronics in place.