I'm a small 32A and 17 years old. Will my breast stay this size or it will change till I turn 20? What should I do?

Not sure what you are asking.  Need more information.  Your breast size may change if you are still developing or if you gain weight.  But if you are done with your breast development or growth, then your breast size will likely remain the same.  To increase your size, you may need to consider a breast augmentation procedure. best wishes.

With the limited information available, and without the benefit of a full history and examination, I would suggest that you exercise patience and wait a few years before you make any decisions about changing breast size/shape.  At that time, if you still have concerns about breast size/shape, best to seek in-person consultation with board certified plastic surgeons who can demonstrate significant experience helping patients in your situation, achieve the types of results you are looking for. Best wishes.