So, I think you did pretty darn well. Any F/D curve above the line at all in an essentially straight limbed bow design is pretty good. And, that is a pretty bow, too.
The flipped tips and almost straight unstrung profile on your bow should give it a pretty good start: high string tension at brace, along with higher early draw weight.
Your F/D curve would be fatter if the bow was longer, had more recurve, or reflex, or took less set during tilllering, etc, but, as mentioned, that may or may not make it shoot faster or farther. Really high humped F/D bows CAN be less efficient.
So, the questions you asked about mass placement have more to do with ensuring you have enough wood to do the job (avoid set and breakage), and in the right places not to slow down the shot. Little to do directly with F/D curve. Geometry allows a badly built, poorly designed bow to show a nice F/D plot while the bow is slowly dying from a crushed belly.
So the answer is, if indeed you needed more mass, it would be wherever the bow took more set than you planned on during tiller. Probably in the form of width, but maybe length, as I didn't see it mentioned.
Likewise, now that you have a curve plotted, shoot some arrows. That F/D curve is adequate (at least) to make your bow a pretty quick little shooter, assuming a couple things. First and biggest is tip weight. If you managed set and tip weight well, you probably have a bow there you should be reasonably quite proud of.
