Thanks for the replies.
Yes Sandra B, I thought they should be 10 1/2".
And yes SusieQ, in my case it doesn't matter a lot. I was just wondering....
And no Gay, I have not measured my strips. That's a great idea. I hope I remember to do that next time I make a 16 patch.
It's probably my seams. Just a little bit off makes a huge difference in the end.