Hello @hollowjoe, I’m one of the developers for the program and I’ve made some changes that will hopefully fix for your issue, but it probably won’t become available until after your assignment is due. So instead, here is an exported version of your project with audio working properly:
https://mega.nz/#!J7AD2AKC!-Js1rbEyN8AqcWcaEnpqgR-ejQVJgme_gKGqZBUAAlA
Hope this helps! If you need to tweak it, you can use a video editor as @JoseMoreno suggested.