I did this same thing on the very 1st quilt I ever made by machine...actually 1st quilt I had made since learning basic hand applique as a young girl from my grandma in the early 1970's. The quilt is Schoolhouse series "Skill a Month", where each month you learn a new quilting technique. Boy was I "in for it"...LOL.
In addition to pressing the seams in the right directions to have them lay flat/interlock, I also didn't know that the "regular" foot that comes with a machine was not the same thing as the quilting foot..so my blocks were all coming out a tad too small. Finally I measured the foot I was using, and then researched more to find the size of a quilting foot..it also being called a quarter inch foot should've been a clue.
... Between that and my not pressing the blocks that taught half-square triangles and flying geese units the correct way to interlock the seams, made this a FUN quilt to make...Since I was basically self teaching at that time, I look at that as part of the problem...and me being a bonehead as the rest of the problem! Below is a pic of the quilt top after I finally got everything figured out...and on the hst blocks, I tried taking them all apart and doing the seams correctly. I ended up just remaking them.
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