I'ma just go ahead and throw my weight behind the rest of the lovely folks in this room.
I think your jaw and chin are both very proportional to the rest of your features. I wouldn't change a thing and let HRT do it's magic.
Besides, I think that if you start tinkering around with your face it will throw the rest of it out of proportion. Frankly, It seems to me that your nose and forehead are slightly larger than most females so having a wider than average jawline works in your favor.
Honestly, I'm very jealous of how much potential you have. Don't ruin a good thing.