It's okay, they do that. Mine have shrunk a few times, but eventually rebounded. I am 11 months on HRT. Growth comes in spurts, and there can be some shrinkage between growth spurts. It's all good.
I'm in the middle of another growth spurt right now. Mine are still little, but they are really cute, and I can play with them any time I want.

I have resigned myself to the fact that I'll never have big bazoomas, but that's okay. They are real.