375cc high profile silicone smooth round - Is this as big as I could of/should of gone? (Photos)

The choice of implant size/volume is a decision which is best made in concert with your board certified plastic surgeons. There are a number of factors which play into the decision including patient desire and chest measurements. Ultimately, your surgeon, based upon his/her exam will be able to guide a prospective patient toward reasonable options.
There are a number of tools available to help a patient make decisions with range offered by their surgeon including sizers, goal photos and 3D imaging. However, it is important to realize that these are "guides" and not "guarantees." They are meant to offer a patient a reasonable estimate on which to make decisions.
3D imaging has become an effective tool for discussing options for patients and narrowing down choices. However, it is important to remember that the imaging is only a simulation. There is no substitute for the experience of a board certified plastic surgeon.
With regards to your specific question, small variations in volume are unlikely to make or break a result. If 375 cc feels small you will likely have to consider something in the rang of nearly 500 cc. Your result seems reasonable, however, marrying expectations to results is something that all surgeons struggle with. It is vitally important to spend time discussing the results of your imaging consultation with your surgeon. As this will help clarify your goals/expectations and guide your surgeon in adjusting those expectations as needed.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

Thank you for sharing your experience — what you're feeling is completely valid, and it's not uncommon to have these concerns after augmentation.