Currently 34B, want to be 38C/34D - is 350cc too much, too little, fake looking?

Thank you for the question.   
Ultimately, careful selection of plastic surgeon and careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, in bra sizers, and computer imaging)  as well as careful measurements (dimensional planning) will be critical.
 ***Given your concerns, I would suggest that you spend additional time communicating your goals/concerns directly with your plastic surgeon, preferably prior to the date of surgery.  It will be important for many reasons, that you feel comfortable that you and your plastic surgeon are on the "same page" prior to proceeding.
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. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining 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. For example, 
I have found that the use of words such as “natural or fall look” or "C or D cup” etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
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, after the use of temporary intraoperative sizers.
I hope this (and the attached link, dedicated to breast augmentation surgery concerns) helps. Best wishes. 

Thank you for your question. It is difficult to give an educated opinion without photos. However, from what you described I believe 350cc may be a good option. The best way to tell for sure is to have a consultation with a board certified plastic surgeon. Best of luck!Dhaval M. Patel Double Board Certified Plastic Surgeon Hoffman Estates Barrington Oakbrook Chicago 

Generally speaking, if placed under the muscle this will provide you at least a two size cup increase (very rough estimate which will vary from one individual to another). If you are uncertain try the rice bag trick under an elastic bralette for a week or two to try it out.