I love this! I know t-shirt material tends to curl, what did you do to prevent that?
When I made my t-shirt quilt.......I used a basting spray.....and basted the squares to matching squares of a stash fabric I bought and then decided I hated. They prevented the t-shirt material from curling by working as a stabilizing material, and I didn't have to trash the hated fabric. I imagine the same could be done with an old sheet. Since the stabilizing fabric is on the inside, you could recycle those old, stained or threadbare sheets instead of trashing them.