If your cutting is accurate then you next should check you seam width. Most patterns call for a 1/4 seam when actually what is needed is a "scant" 1/4" seam..to make that even more confusing is that no two 1/4" feet stitch the same 1/4" seam!
I always nudge my needle over a couple of times..there also is also a product which is a plastic adhesive strip that is supposed create a line that you can feed your fabric along consistantly. Great idea but it doesn't keep sticking...I've gone through 4 pcs so far on my DWR and I haven't scratched the surface, I have only 7 blocks completed. Cut 3 2 1/2" strips 6 inches long..stitch them together and measure after pressing..you should have 6 1/2" if your seam is correct..if it's not pick out the stitches and adjust your needle position and stitch again. Repeat until you come up with the correct measure..write down your needle position settings. Then and only then put together a block..when completed measure it should be the correct size.. Sorry to be so long winded but I am frustrated as well by just what the "scant" 1/4" seam is. So it's very important to check your seam width right off before stitching up a block. Good luck..you'll get it..don't quit.