Looks like you are putting together the helmet by dividing it into smaller sections and then gluing the smaller sections to create the finished product. I prefer this method because it prevents minuscule, incremental mistakes from multiplying and becoming a big problem when reaching the back part of the project when things sometimes can be hard to line up. I've also found this way prevents the pep project from skewing too far towards one side and making the overall project lopsided. This method helps additionally as waiting for the glue to dry can be annoying. Working on several parts can increase productivity by gluing one piece, clamping it with tiny spring clamps (they exist!) and moving on to the next part to be glued.
I have no idea how you are putting it together, but some people cut out all the pieces, make all the folds, then glue everything together. I've found it easier to cut out one piece at a time and glue them together right away. This makes it easier to find pieces and prevents some from being lost entirely. Having the Pep Designer open helps so you can click on the piece you need in the 3D portion, it highlights which page the piece is located on the 2D outline, and from there finding the part is easy.