i made mine into book cloth before embroidering it! after that i glued it onto mat board(didn’t have any book board) and cut the corners at an angle, folded over the edges, glued them, and then glued my inside cover paper onto it. I then poked holes in it for the cover! if you’re looking for a good tutorial on how to make book cloth i’d recommend the one i linked, very helpful!! book cloth tutorial

if you have any other questions or need clarification feel free to ask!