Hi Shane!
Dagger are without a doubt the most difficult knives to make correctly...most of it due to what you mentioned...symmetry.
On a single edge blade/knife, you have two planes, and we do our best to make each plane a mirror image of the other. With a dagger you have two planes per side, for a total of four. Not only do you have to make the two planes on each side mirror images, but you also have to make the two planes on each side mirror images of the other.
The best advice I can give you, is to draw the blade on a piece of stiff card stock, the fold it in half, exactly on the center line of the blade, and use that as your template. There are a lot of things to keep track of, so be watchful. When I built my MS dagger, I did it three times, trying to forge out the blade. I finally gave up and built a billet, surface ground it, and then scribed every line on the thing, and did it all with files and sandpaper.