Thanks to all who answered!
Those of you who mentioned stretchiness made me race to check. I hadn't noticed any stretchiness, but sure enough, it stretches when I pull, more so than the cotton. I am more concerned with how that might affect my learning to use HSTs than anything, but now I know not to even try using them as larger pieces.
Wear is something I hadn't even considered. I'm making it to fit a bed, but lol, I'm not sure I'd want to sleep under my learning sampler. Hmmm, maybe it'll be a wall hanging for my computer/quilting area. Well the goal is just to do it for now. I won't worry about a couple of pieces outlasting the rest.
Pilling is something I'd want to avoid, though. It didn't pill in the pre-wash, but I know that's no guarantee that it won't in other washes.
LOL, no I can't see ever entering my first real quilt in a contest. No issue there!
Thanks for the tip on covering it with cotton for ironing. It occurred to me that that must be safe, since you can use polyester batting, which I did for my quilting class project. No problems ironing over that, and of course it was covered by the top and backing layers, which were cotton.
So I guess I'll go ahead and use it. If I find the color in cotton before basting the quilt sandwich, I can always remake the blocks, which won't be such a big deal as there will only be two of them to redo.
Thanks for the link to Hancock's. I don't buy online or mail order, because the colors so often aren't as they appear on my monitor or in a catalog. I did go and look, and unfortunately, they don't display them in spectrum order, so you have to hunt through the whole thing to see your colors, and then it's hard to compare similar ones. In any case, I didn't see the color I want.
Maybe it's just because I'm new to quilting myself, but it seems to me quilting is growing in popularity. It may be the next needlework trend. There's a good business opportunity for someone who wants to manufacture quality cottons in all colors along with prints at affordable prices.