I stopped cutting corners when I took a class with Peggy Sagers, from the ready made clothing industry. My experience was that cutting corners created the potential for fraying fabric, and eventually holes in the corner [using Fray Check can help with that, but seems like an unnecessary step.] Instead, I stitch right off the end of all seams, which creates a grid at the corners. With an iron, I fold the fabric on the seam line, using the thread as a support, in both directions. Iron the corner flat; I hold the corner between my thumb and finger while turning, and use a tool [there are many] to straighten out any bunched up fabric, gently pushing out the corner. Other than that difference, very helpful video!
Thank you for letting me know, I would suggest searching for abc fabric panels on Amazon or a fabric store, here is a link to it, www.amazon.com/s?k=abc+fabric+book+panel&ref=nb_sb_noss Thank you for watching!