With a pattern like that seam allowances "the same" isn't good enough. They have to be a scant 1/4". In other words, the seam has to be just so that the seam allowance and the thread line is 1/4" plus accounting for the fold from pressing. It's too late now but before your next project, you can do a test to determine if your seam allowance is correct. Sew 3 1.5" strips together, press as usual, and make sure the center is exactly 1". If not, keep adjusting your needle position until it's exactly 1".
Also, all feet are not necessarily going to give a 1/4" seam allowance. I have a patchwork foot that is supposed to be a perfect 1/4" but I had to adjust my needle position a bunch to get it just right.