One of the things I learnt from this project (other than to not look like a quilt) is that I should have pinned and sewed discs onto the garment in stages. I had not done this and so I kept getting poked and scratched by the sewing pins!
Once I had the discs sewn on, I turned the shirt inside out, and cut the shirt below the sleeves. The shirt was then sewn up, as indicated in the image below. And, that's it!
I'm glad I made this pillow cover, and not wear it! Hope you agree :-)