Is there true that a 400cc will really look like a 350cc on me for Breast Augmentation?

For your size I'd suggest sticking with 350cc. However, discuss your concerns with your surgeon as they'll be able to help you better based on a physical examination.

If you are uncomfortable with the implant that should be a red flag for you.  That being said it is not that differeent a volume.  Were you able to look at it on a simulator? That helps ease patient's fears....

Thank you for your question and I understand your concern.  There is a significant difference in a 400 cc breast implant in terms of base width when compared to 350 cc.  Personally I do not subscribe to the fairy that breast implants will look to sizes smaller when placed under the muscle.   If your concern is looking to be, and since you are petite at 90 pounds, I do not think there is a problem with choosing the size that you're most comfortable with which is 350 cc.  That should give you a nice full result.