Well, I don't think it means anything in particular. I had some growth after a few weeks on spiro alone so I don't think it is that unusual.
Most trans girls don't naturally get much more than a natural B (from what I have read, though there are exceptions). Some say you potentially will end up about 1 size below your nearest relatives, but I'm not sure that is true. Perhaps if you had them as long as they have they might get that big, especailly if you keep gaining weight as a lot of woman do these days. But we are starting rather late in the piece. On the plus we are likely to be perkier compared with other women our age.
Unfortunately you can't do much about it. Except if they get so large they are dibilitating you could always opt for a reduction.
Watching your weight will help some. Otherwise I think you will need to learn to love what you get. Part of being a woman I'm afraid, just part of our lot. I really don't think you will find them a chore, they will be a symbol of your femininity. Chances are they will feel good to hold in the dark.
Hope you enjoy your new body! Welcome to puberty.