Handle Screwed On

Hi, I appologize for the lack of piuctures since I'm transitioning to a new phone. I spent about 2 and a half hours in the shop starting at 4, drilling a fourth hole in the handle and drilling holes for rivets in the buckler's plate. I had much help and instruction from Don in all of this, especially because he knows how to use the drill in ways that I don't. Attached the handle with screws and nuts to see how it all fits, and it's looking pretty nice. I am quite sure, however, that the handle is not thick enough for a good grip. The buckler is of thin-gauge steel and therefore not really suitable for fencing in the first place, but with the thin handle it rotates in the hand too easily. I don't think I feel like forging a new handle at this late stage, but if I were to make another buckler I would choose much thicker stock to begin with and make sure the handle was thick enough to be immediately serviceable. The only question now is how to modify the current handle to fill the hand, and prevent it from twisting in the hand too easily. It's meant to replicate a fighting weapon; it has to do what I want it to do, not rattle around in my hand.