It happens to the best of us. When doing 1/4 inch seams, I find that most pattern actually need scant 1/4 inch seams to account for the thread and fold over. Unless your machine has a perfect scant 1/4 foot like my Bernina, you will have to adjust your seam size. Instead of measuring from the stitching line over to the edge for your quarter inch, make sure that the sewing line is just inside the quarter inch. Hope this helps but if all the blocks are the same repeat pattern in a quilt then the 1/4 doesn't matter. If all the blocks will be different like a BOM you do need to work out the seam allowance before proceeding or all the blocks will come out different sizes depending on the number of pieces involved.
BUT it's is still not a disaster if the blocks end up odd sizes, just set them in a "wonky" positioned sashing or adjust the sashing sizes and resquare them when finished. Good Luck and keep quilting!