My pillow was 14x14 so my first piece of fabric was cut 15x15. For the back I cut it 15x22. The 22" is one and a half times bigger plus 1" for seam allowance.
Cut the long piece in half and fold down one end on each piece. I just ironed it to keep it down. I didn't bother with pinning. Sew this piece down.
Now just arrange everything. Lay the pieces right sides together. If you do "fancy" stitching make sure that piece is directly on the 15x15 fabric and the other piece will lay on top of that. When you flip it out, the fancy piece will show and the other piece will be hidden behind.
Then all you have to do is sew all the way around. Trim the excess paying attention to the corners. Insert your pillow and you're done!
I have some Dora fabric that I plan on making too. I need to buy another pillow though. I think I might buy a rectangular one, or I might just go ahead and make another square one and when my little one wants Dora, I'll just change the pillowcase.
I hope you make this. Enjoy!
Apple