You have more Pics of how you covered?? I have that same exact bed build.
Discussion
With the framed cover?
If so, I just built a rectangle frame the same dimensions as the raised bed. Then lay the plastic on it and staple it. Lay the frame over the bed and put a few pavers on the corners to hold it in place. I didn’t want to affix it permanently to the bed because it would block one side
Ah! Sweet. Great idea.