Is there any problem with a quilting template that is a tiny bit off?

I have lots of plastic canvas and I am thinking of making my own templates for quilting squares. For instance, when I measure for a 6" square it comes out to 6 +1/16th. Is that gonna cause any real problems? Also any fabric stores on line that any of you recommend?? I ordered some quilt fabric form Jo Anns and some from Quilt in a day. I appreciate any ideas since I am very new to quilting.