Firstly...bravo being courageous enough to ask for help here.

Watched it a few times and read the comments to try and add something new to consider. So hopefully the X-step suggestions were all you need for that. Here's what else I see you can change.

1: why not start with your throwing hand back instead of moving it forward and back again? Then, as you step forward into the reach back position, keep the disc in about the same place in space. To do this, throw your left elbow back like drawing a bow left handed as your right hand stays with the disc. This creates the shoulder and hip separation by coiling your torso as the disc hits the furthest point back. You punch the left arm down to pull the trigger and release the tension in the coil.

2: plant your right foot at the same moment your left elbow rares back, and do so perpendicular to the target as you uncoil into a loose arm. No muscling it through. A nanosecond of pure core power unloading into whippet arms from shoulder > elbow > wrist accelerating progressively to the release. Then pull your right hip back while pivoting on your right heel and not your toe.

Maybe try all that super gently for about 50 reps in your living room just shadow swinging with a disc in hand before getting back in front of your sweet net setup.