Betty, on certain patterns it will not matter. For instance, a Rail Fence block, where you sew three strips together. If the measurement is supposed to be 6-1/2" and yours is 6-1/4" wide, just cut the blocks 6-1/4" in the other direction so they are square. Your finished quilt will be somewhat smaller, but if you don't tell anyone they won't ever know {smile}.
Other patterns, however, are more critical. Certain stars blocks may have their points cut off - that type of thing.
Did you know that the ruler you use can make a difference? See my post here
http://www.quiltingboard.com/main-f1...l-t142312.html
And I also have a post on how to achieve that accurate 1/4 inch seam here:
http://www.quiltingboard.com/tutoria...ce-t89997.html
Keep in mind that you don't really care that the seam on the backside of the block is perfectly 1/4", it's the measurements on the FRONT side that matter.
Good luck!
Andi