The next step is to use a hot glue gun to attach the strips you cut to the edge of the rocket shape. This step is fiddly! If you’re doing this project with kids it might be an idea to use a cold-melt glue gun, or make do with traditional paper building methods, tape or a Makedo cardboard toolkit.
Position the card strip around the edge of the rocket shape and cut it to length. Then put some sticky tape or blue tack at each end to secure it in place. Run a bead of hot glue all along the bottom edge of the corner to secure it in place. It's also a good idea to glue up the joins of the pieces of cardboard so that the light doesn't leak out.
Do this for all the bits of cardboard. Then do another strip along the dotted line of the template, to separate the fire from the rest of the rocket (otherwise the different colours of light will merge into one).
If you're using a USB cable to power it (not a battery), you'll need to test-fit the Circuit Playground Express into the bottom of the rocket and cut a little slot for the USB cable to pass through.
You can also paint or decorate the inside or outside rocket at this stage. Just bear in mind that the inside of the rocket will be covered with paper by the end.