The only skill i can't do in the compulsory floor routines is the back extension rolls. I either end up in an extremely arched handstand and then fall back into a bridge, or a end up flat one the ground with my hands under my hips, laying on my stomach. It always hurts my shoulders, too. Is there something I'm doing wrong? How can i fix this? I can do a backward roll to handstand if i bend my arms, but not if i try to keep my arms straight.