I'm not sure I understand your problem. Is the countersink off center or the tang bolt hole at an angle? The advice above for centering a countersunk hole is ok, but if it is the hole itself, just tap it, add a short piece of correct screw stock, peen it well. Then file the surfaces flat and drill again at the proper angle. If you are drilling in the same spot, you'll never see it. I often use this technique if I drill a little off center.