Heating a bow with a heat gun is really running a fine line of burning the wood and bending. You have to get a feel for it, watching the wood sweat, getting glossy when the resin starts to come to the surface, and not smelling burn't wood instead of popcorn cooking. You need to bend a few pieces and get a feel for it. Sometines it takes a few bendings between cool down sessions to get what you want. And sometimes you just can't do it without destroying a piece of wood. And yes, rehydrate before bending.
Heat treating instead of bending is a whole different story and when I do this I'm trying to burn it but not deep but even. you have to know when to move the gun, again, by experiance.
I hate to see your bow broke but I have no doubt you will have a fine one soon with this attitude. Everytime you break one there is a reason and one more step in the learning curve.