Like Pearl said, you should not have changed the color of the wood at all. You can get it plenty hot enough to bend with the heat gun, without scorching, by moving the gun in a slow sweeping motion, about the same speed you would slop paint on with a brush, never stopping, from about 4" away. Heat all sides. Heat it until it's too hot to touch/hold, perhaps an additional minute more, then make the bend before it begins to cool. If it begins chaanging color, move faster, move the gun farther away, or both.
Keep in mind, you don't only want to get the outer surface hot, you want it hot all the way through, and wood is a poor conductor, so don't only concern yourself with the surface temperature. As you warm the wood, imagine the heat slowly, slowwwwwly soaking into the stave from all sides. You don't want to scorch the outside before the center is hot enough too. So, of course thinner parts take less time, thicker areas like the handle take longer.
With the size of material you are working with, it should have been hot enough to bend in 7-10 minutes... depending on how long of an area you are heating.
Your dimensions should not have mattered. The moisture content was fine. I would not use steam. I try to follow the popular advice of "dry heat for dry wood, wet heat for wet wood".
I think you probably heated it too close, too slow, too long... or all of the above.
Why don't you try the other limb, for practice if nothing else?
How about the end you tried to bend, is it ruined?