nanna - I feel your pain. I used to have this problem a lot too. I THINK the problem is 1/4 inch seams, and possibly stretching the fabric a little when sewing. Now I measure the 3rd border, hold it up against where it's going to go, just to double check. Then I sew the first cornerstone on, press and check again. Then I sew the second cornerstone on, press and then check again. THEN, I pin the seams where they are supposed to go and then pin the heck out of the whole rest of it. I think this is one of the only time I use pins. Then, if your sewing machine can regulate the pressure of the presser foot, fiddle with that a little bit. If my pressure is too high, it seems to push the top fabric and un-align all my hard work. Good luck!!