So I'm working on making a playground slide out of sheet metal, but when I try to add bends to convert the part into sheet metal so I can flatten it I cannot get it to flatten for the life of me. It keeps telling me that one of the bends has failed for some reason, yet I cannot for the life of me figure out what I am doing wrong. I'm doing exactly what this tutorial video on YouTube does (Solidworks Sheet Metal Elbow - YouTube) but SolidWorks doesn't like it.

At first, I thought the problems were from there not being a completely flat surface on which to add the bends, but I manually added a flange to section 18 and it still didn't go.

Any suggestions?