450cc, under the muscle & asymmetry, how to fix it? (Photo)

We always say the breast are sisters not twins - without seeing your preop photos it's impossible to know if this asymmetry was present before surgery. Just adding volume can make little asymmetries more apparent because everything is bigger. I would assume you likely had nipple asymmetry baseline and without adding a mastopexy or a lift it would be impossible to even them out.
More photos and or an exam would be necessary to assess volume asymmetries or concerns for capsular contraction. If there is a substantial volume difference you could consider different size implants to balance things out.
Capsular contracture would require capsule removal and a new implant. Based on this one photo that does not seem to be an issue though.

Dear nouhaila,
I understand your concern. However, without a proper assessment, it would be difficult to determine what is 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, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

Your breasts are asymmetrical in the position of the nipple-areola complexes. At this time, I recommend explantation and lift using The Bellesoma Method. The implants are removed, your breast tissue is reshaped creating upper pole fullness, elevated higher on the chest wall and more medial to increase your cleavage. Vertical scars are avoided, nipple sensation (in 95%) and the ability to breast feed are maintained if not injured during your previous surgery. Later, fat transfers can be performed if additional volume is desired.

Best Wishes,

Gary Horndeski, M.D.

Sometimes, asymmetry after surgery is because of pre-existing asymmetry. You would have to look at your before pictures to know. I would be curious whether your right implant feels higher/tighter than the left. If so, that could be a sign of capsular contracture. This is a complication related to excessive scar tissue around the implant that is triggered by bacteria in your body. It can happen rather quickly after surgery, or it can happen years later.

The importance is that if you have capsular contracture, you would need to remove the scar tissue completely before putting a new implant in to optimize the chances for good symmetry. If there is no excess scar tissue, then it's hard to know whether just exchanging and repositioning the implant would be enough or if you would also need a small lift around the areola to improve symmetry.

I would not go larger and even consider going somewhat smaller. The pocket of the higher implants can be released to let it settle down better. Once the implant is lowered, the nipple might be in the correct position.

Dear nouhaila,
Your breasts are asymmetric. Most of the world population has asymmetric breasts. We are missing your pre-operative photos in order to comment on whether or not your asymmetries were present before. A small lift, either periareolar, or lollipop would create better nipple position symmetry at the expense of scars and possibly creating breast shape asymmetries. Good luck!