A finer thread is needed for those tiny pieces. There is not much room for error. Especially in 6 1/2 inch blocks.

I recently made a sampler quilt for my daughter made of 4-1/2 inch finished blocks, so accuracy was a necessity! I found that my accuracy went way up when I used tiny drops of glue (plain old washable glue in a bottle with a tip that put out very tiny drops; I found a set of three on Amazon). I placed tiny dots of glue at the edges inside the seam allowance, put the two pieces together, pressed with a hot iron to dry quickly, and then allowed to cool before actually sewing them together. I used 50 weight thread in the top and 60 weight thread in the bobbin. I used a scant 1/4-inch or 1-/4 inch seam allowance - whatever got me the finished block size called for.
I wish you well with you sewing!

I usually cut a bit big and then trim. right now I'm making "nearly insane" but swapping or changing a few blocks so that I don't have less than 25 pieces per 6" block.

As usual, I found it by googling for it. Several sources came up! Hope it works for you!

I'm working on a quilt right now that has some 1 1/4 inch squares- pretty small!
I used a finer thread and sew just a tad inside the line. So far so good.

I have been making 4 1/2” Easy Breezy blocks, I use a 60wt thread on top and in my bobbin and I try to make a scant 1/4” seam.

I use a lot of 1.5" squares in sashing to make 4-patches at the join and I make sure they are starched board stiff so they don't distort and I also use a 60 weight thread and a smaller stitch. I also try to do as much strip piecing as I can so I don't have to handle the small blocks individually.

I use my Accuquilt system that lets me make the perfect 11/2" square.

That's actually a wonderful idea! I have tried tiny squares only for things like mug rugs, and I don't enjoy it. Right now it would be a tangent away from UFO's, so I'd better just bookmark this thread and save it for someday.

Okay so I am the odd one here. I love tiny pieces. Currently working pn Sue Garmen Oh My Gosh quilt using 1" strips for the 4p and 9p needed in the blocks.Need 440 4p and 550 9p. Have about 150 4p and 200 9p to make yet. Using all from scraps but using strip piecing techniques. This one uses 3/4 " pieces