I can't put together any block without squaring it up, but in the video, Jenny doesn't square hers and some look quite off. I would think for that quilt to come out right, the blocks need to be 5 1/2". How many of yours need work?
Same machine, same thread, same everything and yet even a nine patch can be almost a 1/4" off. So maddening! I recently sewed enough 9 patches for a quilt and they were all small. I had used a different machine! They couldn't be used as the other block was snowballed, so I had to start over.

If my blocks were that little "off" (and mine usually are!) I would just ease them in, as mentioned above. I don't square up every element of every block and do try to square up big blocks, but, like you said, same machine, same thread, etc, and they are not always exact. And somehow when I am done with the quilt it is pretty much square, just needing a bit trimmed here and there. I can't figure it out either!!

I don't square blocks. When I tried it, my blocks just kept getting smaller and smaller... Now I make a couple of extra blocks for the quilt and choose the best. After saying that, I do NOT sew for entry into quilt shows. My audience is family and charity quilts, and I have never gotten a complaint - except from my son! Listened to him for a few minutes and said, "Give it back!" He said, "No! You'll never make me another one!" He has a hard time just saying thank you...

Another comment -since I got my accuquilt studio, my blocks are more uniform. My thinking is that it has to do with cutting accuracy.

Were you using precuts? I really prefer cutting my own pieces/strips/squares over using precuts which are so often not cut precisely.

I just line up each end of a square and hold it until it is sewn. Seems to work for me. With all the sewing I do since I retired first of year I have gotten more exact and not having that problem much.

I (finally!) learned to measure my units and not my seams from a Quilty video. Marianne Fons joined 2 2.5" squares, pressed them and then measured to make sure they were 4.5". The video is called Boot Camp: 1/4" Seam Test. For a long time I just measured my seams, they were 1/4", but my blocks/rows didn't match up. It was totally frustrating! I watched that video and it was a "Duh! Why didn't I ever think of that!?!" moment. I sat down and did the same thing and adjusted my needle position until I got the 4.5" measurement and things have lined up much better ever since and I do a lot less trimming and seam ripping.

The fist thing I check when a block is off like this is the pressing. Did I not open a seam enough and get an off seam crease.

The next thing I consider is spray starch and spritzing with water after the fabric is cut. If the fabric isn't washed and or starched before cutting it can shrink when any moisture is added. my experience has taught me to wash/ and starch before cutting. Then any additional moisture like another spritz of water or starch won't shrink the fabric.

This won't help for your current project but future ones could see less distortion. and please remember you are not alone in this situation. Just about all of us can say we have experienced off sizing.

Squaring up aggravates me the most, but if I am to be a better quilter, I just do it!!!

I don't square up, I just go with what they are. All my quilts come out square and beautiful.

Glad you asked that question,I have that problem too seems like the more careful I try to be blocks are not always square. Will try all of this advice Thanks