I applaud your work so far, but it appears you made a major design flaw. Leaving the handle area, the handle thins to working limb thickness way before it widens to full width. When it is thin AND narrow, it creates a weak area, greatly increasing the risk of breakage there.
Instead, the handle should gradually thin, and ultimately come into working limb thickness beyond the flares. That is to say, on the limb's side of the flares, not the handle's side. Does that make any sense? In other words, the piece you added on for your handle should have been considerably longer, extending beyond the limb's flare to full width.