First, build up your back and shoulder flexibility by doing bridges. Try to push higher and higher and hold them for longer. Once you have a better bridge, try doing backbends on soft serfaces, a mat, a bed, even a couch. Don't freak out, just go for it! As long as you do it somewhere soft, you won't get hurt. If you can do handstand-to bridges, they also really help, because it is like a reversed backbend, so it helps you to have flexibility in the right places.
Hope this helps, and good luck!!!
