Oh Ginny - could be ALL OF THE ABOVE! If cutting is off, then the block size is off. If you stretch the fabric, especially a problem when sewing on bias edges, then the block size is off. I've even had a problem when using two different rulers (from different companies) and the block size is off. Then there's the "scant quarter inch" issue. Don't get me started.........Best thing is to take three precisely cut 2.5 inch by 3 inch rectangles and sew them together on the 3 inch sides. Measure when done and you should have a 6.5 by 3 inch block. If you don't, and you know for certain that your cutting was accurate, then it's your sewing. That means you need to "find" your quarter inch. Take a piece of grid paper, 4 squares to the inch or a lined index card. Put your needle EXACTLY on a line and see where the next line to the right of it falls in relation to your sewing machine foot. That is where your fabric needs to flow under your foot in order for your seam to be a quarter inch. If a block has many seams in it, it's best to have your seams be "scant", or ever so slightly short of a full quarter inch. And some people even use thinner thread in order to not take up excess measure in the seam (once it is pressed over). Oh, and pressing can also turn your block into the wrong size. Remember to press, not iron. And check your block measurements at interim steps in the block. Square up if necessary. There should be a full 3 credit college course on this subject - so keep practicing until you get it.
