I'm worried about transitioning now because I'm afraid I won't look how I want to look.
What 67 Rover said.
It's a garbage in, garbage out deal. If you're a 240 pound, six-foot-one dude, it is physically impossible for you to be convincing as a chick. If you are a five-four chick, fat or thin, you're just going to end up looking like a bull dyke, or at best a dude of unimpressive stature that's either a butterball or scrawny but with an odd preference for baggy pants to hide your hip bones.
If your actual skeleton and musculature really is a lot like a reasonable average of what you're going for, you may be able to actually pull it off, at least for initial impressions. You're still not what you're pretending to be, but at least you can pass for awhile and fool yourself.