so your having problems mirroring one side to the back side? ok well what i can do since im not exactly sure what you mean still. i will make a video of me doing the entire thing, except drawing the sword ill find a screen shot.
*edit* from what i see on your sword you duplicated the side and then attached it to the back of the model like you should have...but both sides were flat so your end result was flat also... so let me make you a quick video.
*edit* here is your video, i showed most steps except one important one that would take too long to do on the video. when i duplicate and mirror from front to back, you need to weld each vertex to the first half of the model, so select the front and back vertex one by one and hit CTRL+N to snap them together then CTRL+W to weld them together, make sure that you regroup all of them so when you apply the texture its not only half the model. hope this helps, good luck.
