I have 286CC implants but after three weeks, they look smaller than I wanted. What's the appropriate size for my anatomy?

It is important that the plastic surgeon in the patient are in agreement upon the final breast size before undergoing the operation. There are sizing systems are very useful in achieving this agreement.

Your height and weight indicate that you are a petite person. The most important determinant of an implant being the right size for your anatomy is the base diameter of your breast and the implant you choose should fit within that - it should not be too big or too small. For a given base diameter - different volumes and sizes of implants are available - the higher the profile, the more the implant sticks out form your body, and the larger the volume. When it comes to soft round silicone gel implants, moderate profile implants have a good balance of full volume for the diameter, and placing them under the muscle helps to keep your overall look natural and minimizes the risk of visible rippling. An implant between 250 and 300 cc should definitely give you roughly a 2 cup size increase in a way that keeps your risk of long term complications low.At only 3 weeks after surgery, you cannot judge the final results of your augmentation. It takes the muscle at least 3 months to fully stretch and relax over the implant. At three weeks the muscle is still very tight and squeezing the implant against your chest internally. As more time goes by, the muscle relaxes, and the implant falls into place in a more relaxed position - with this relaxation also comes a fuller look. Bottom line - be patient, follow your surgeons instructions for postoperative care, and give it at least 3 months before you judge your final results.

and it should be up to you to make a decision as to what you want when fully informed.  But since surgery is water under the bridge, it is always best to wait and heal and allow yourself time to adjust and better appreciate the benefits you have obtained with what you have.  Perhaps your friends tell you it doesn't look any different... but have these friends also viewed you without clothes?  You should have an appreciable difference and benefit from the size you have.  And if you want more feedback, you can always repost with a photo.

I'm sorry to hear about your concerns after breast  augmentation surgery.  Although,  online consultants will not be able to be of much specific help to you, it may be helpful for you to know that a significant percentage of patients ( early on after breast augmentation surgery) feel that they are “too small” or “ too big” only to go on to be pleased with the longer-term outcome of the procedure performed.   Therefore, best to evaluate the outcome of the procedure performed about 6 months down the line. Generally speaking, the best online advice I can give to ladies who are considering  breast augmentation surgery ( regarding breast implant size/profile selection) is:1. Concentrate on choosing your plastic surgeon carefully.  Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.  
2.  Again, have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or breast implant size/type/profile will most likely help achieve your goals.
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or "C cup" etc means different things to different people and therefore prove unhelpful.
 Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.  The use of computer imaging may be very helpful during this communication phase.
3.  Once you feel you have communicated your goals clearly,  allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery.  The use of temporary intraoperative sizers with the patient in the upright position are very helpful.  Best wishes; hopefully you will be pleased with the long-term outcome of the procedure; if not, it is likely that revision surgery will be helpful in achieving your goals.

Over the next 3 months your breast implant shape and size will change significantly.  The implants should drop beneath your nipple areola and look much better.Generally speaking 280 cc implants should increase your cup size by a factor of 2 in the bra you are wearing before surgery.  Of course you need to discuss this in detail with your plastic surgeon.