awning clamshell cover problem/cord size?

I bought a trailer that was missing the whole awning except a piece of one arm and the aluminum clamshell cover that protects the awning.  It was a dometic power awning on a 2022 Rockwood signature.  SO I order fabric on amazon, but when I received it and tried to install the fabric in the awning clamshell it wouldn't slide in because it appears the diameter of the clamshell opening slot was smaller than the polycord on the fabric.  So I tried it in the awning rail instead after removing the clamshell, and surprisingly the fabric slid in like normal.  But I'd like to have the clamshell.  Anyone run into this problem before or know what size polycord would fit a dometic clamshell?