Motiva, under muscle, 205cc - why are breasts still firm 6 months post-op?

Hello. No need to worry. You started out with an A-cup, so you probably did not have much tissue to begin with. This means it will take time for you breast tissue and skin to loosen up and adjust to your new size. This will get better with time fir sure.
You just need to be patient and enjoy your new breasts!
Dr. Miguel Mota

Dear Fabulous8441,
I understand your concern. However, without a proper assessment, it would be difficult to determine what went wrong. It is best that you visit your plastic surgeon for further assessment or ask for a second opinion. Only after a thorough examination, you can get proper recommendations and advice.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

I understand your concern.
It is difficult to say if something went wrong in your surgery, as far I can tell just by the description of your text, I think you may have a breast augmentation with your implants under your muscle, this could be the reason of the firm sensation and as they have the sternal bone (and the pectoralis muscle insertions) as an anatomical limit you can't make them come together.
I really recommend you consult a Board-Certified Plastic surgeon that could guide you in this process, I hope this information helps.