Uh, your shoulders' muscles should thin down/stop growing. The bones should stop getting larger. They might shrink a little, with a small chance, because you are still in puberty.
As for transitioning, well, this is hard for everyone. Most people start hormones and whilst they do their work (they take a few months, up to 6, to do any "definitely obvious" things, usually) they continue to present as male. Then there's a decision, you have two choices:
-Either you just decide to continue on as female one day. This may be dangerous because people are mean, but it's also the most honest and, if you go through the social stuff, can be great. Though doing this may destroy your woman's image forever, meaning you will be "the trans". If you have a lot of good friends, you can do it basically unharmed, I guess, but people will still know.
-Either you "start a new life" by changing schools or such. This is hard because you have to break from your past and lie / stretch the truth a lot, but it also has the highest chances of letting you have a normal life.
My choice is probably the second (I may still change my mind, but I'm still being stalled for HRT, so hard to know just yet), because I yearn for a normal life. It's a hard choice, but all big choices are, and you need to choose someday.
EDIT: Shoulders and height should not be affected normally. However, you are still in puberty and in it (and with luck, a little after it) there can be some backtracking, which is awesome. As for shoulders, everyone can get effects, since a part of shoulder width is muscle and this can be reduced.