Will 290cc silicone get me from a B to a full C?

Sounds reasonable. You are quite slight and a 290cc implant should get you to a full C. Cup size is the most convenient way of talking about breast size, but the way one woman wears a C cup bra may be completely different than the way another woman does. I assume you’ve tried many implants on during your consultation.  If not, you should try 290’s and other sizes on with your own T-shirts and blouse over them. I think this is the best way for the patient to know what the results will be like, Typically, the PS or his nurse will assist you in the sizing,  and if they’re experienced and have done this hundreds of times, you should get a feeling of reasssurance. If you don’t, I would step back and reassess. Best of luck.

 After I measure and discuss goals with my patients, we then look at pictures of women with similar measurements with different size breast implants. My patients tell me that this process is very helpful in determining what size breast implant is right for them. 
Dr. Ted Eisenberg, Board Certified Plastic Surgeon and Author

My best advice: more communication.
It is definitely worth spending more time (prior to the date of surgery) with your plastic surgeon to discuss further.  As you know, 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.

One question that might be helpful for you to consider: would you be more disappointed if you are slightly too big or slightly too small after the breast augmentation procedure?

Ultimately, 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.

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 "full C cup” etc means different things to different people and therefore prove unhelpful.

There is no accurate/reliable/predictable correlation between size/profile breast implant utilized and cup size achieved. For example, I do not think that the generalizations of "200 cc equates to 1 cup" hold any validity or are helpful in any specific or practical way.  In my practice, I ask patients not to communicate their goals, or evaluate the outcome of the procedure performed, based on cup size references. 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 helps. Best wishes for an outcome that you will be very pleased with.