There is a rare patient who does not respond well to Sculptra. It seems as though if this happens, it is more likely to be an older patient, say in the late 70's or older. Even these patients can respond if treated again, however.
Your experience is very curious, and I would encourage you to ask your doctor to discuss it with the manufacturer of Sculptra.
If the 10 cc were in one bottle of Sculptra, the dilution was appropriate. On average, 1 bottle of Sculptra is required for each decade of life. For example, if you are 60 years old, you may require 6 bottles of Sculptra injected over a few months and the results should last 1 to 2 years. Speak to your physician to discuss why you are not having the desired effect. If you are still concerned, seek a second opinion. You may require a different treatment to achieve the results you would like.
The standard dilution is 9 or 10cc for one vial of Sculptra. I have no idea why you would need 20 injections over the course of a 2 1/2 year period. Please get a second opinion by a board certified dermatologist with a great deal of experience in cosmetics.