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

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.