If you are redoing seams over and over - maybe you need to go back further -
Are your pieces cut as accurately as possible? are your pattern pieces/templates correct? (Sometimes they are wrong.) Is there an error in the directions? (Sometimes that happens, too.)
Some fabrics, if unwashed, do shrink when they are pressed (with moisture) -
Yes, I do try for accuracy and precision - but I feel that after three tries, I need to recut the fabric pieces because all that stitching and unsewing has weakened the seam line.
And why did I mention the other things? Because I have encountered them. Some of the things one learns from experience.
I also will see if there is some other reason why things aren't working - because I usually get fairly close to what I am expecting to get.
Perfection? not possible.
I usually try to do as well as I can do - but there are times - when good enough - IS - good enough!
After three tries, if one intersection out of several just won't line up - and everything else is - so be it.