Concerned about and uneven butt result.
You should definitely notice some early differences between sides. It sounds like you should clarify with your surgeon your concerns. Fat grafting entails taking excess fat from the areas of your body you consider problem areas and transferring it so that it has the best chance of survival. This will help add shape and volume. There is a period of recovery needed for the fat to settle and make its home in this new region of the body. It does take time for it to soften and also for the skin to relax under some of the stretch. Again, I would advise consulting again and/or considering obtaining a second opinion.