Very nice looking pack. Did a great job with the pep. But if you want any type of durability you will need to have some structure to this. You will need to use fiberglass, card board or something & then use a resin to reinforce the pack. The card stock will not hold over time if you are planning on wearing this.
After adding some type of structure you will need to use some type of filler to smooth things out, such as bondo.
There are many examples of these processes in various threads here.
Great job man! That looks first class. You got some skills brother....