How do i know that my scheuermann's disease has stopped getting worse or stopped getting curved ?! how can i come to that conclusion eventually ?

You're a grown up.: scheuermann's is a disorder of the uneven growth of the spine. Think plants. If they grow crooked, you can stake them and they turn out straight. BUT if the growth is fixed/completed then nothing further can be done. Obviously some aspects of this are quite variable, but the underlying principles stay the same across individuals.