Breast augmentation 5 days ago and they look smaller than I expected. Will the size increase?

I'm sorry to hear about the concerns you have after breast augmentation surgery. You should be aware that it is not unusual for patients to feel that they are “too small” or “too big”,   early on after breast augmentation surgery.  Most patients who feel this way ultimately are pleased with the results of surgery in the longer term. Many patients who feel that they are too small immediately after surgery find, as the breast implants “drop and fluff”,  that the breasts actually appear larger to them.
 I routinely ask my patients  to wait at least 3-6 months before   evaluating the end results of the breast augmentation surgery.  This waiting time allows patients to (uaually) physically and psychologically adapt to the new body image.  
Obviously, it is best for patients not to be making important decisions ( for example about the results of surgery and/or the need for additional surgery) while they are experiencing the common post operative emotional “ups and downs”. In the longer term, if you still remained displeased with the breast size, communicate your concerns with your plastic surgeon in a calm and constructive fashion. Together, you will be able to determine whether increasing breast size can be safely done. Remember not to communicate your goals in terms of achieving a specific cup size, which can be a source of miscommunication. Best wishes.

It is really early to be trying to evaluate size. Assuming these are under the muscle, the pectorals will compress the implants until those muscles relax to accommodate the new volume. Often, patients find that the breasts appear larger once the implants "drop". Without photos and measurements it is difficult to evaluate your judgement of a "C" cup appearance. Depending upon where you started, it is tough to imagine that size implant not making you larger than that. Better reassurance will come from your own surgeon.  Best wishes