if you are hand piecing= how are you going to square up without clipping your seams? you could do some (fudging) on the sashings, to bring the blocks all up to the same size when the sashings are attached instead of cutting your blocks. you might want to wait until all the blocks are done so you can work from the smallest one- in case they wind up being all off a bit-differently- i have a 12 block sampler that wound up every block being different---
i would adjust-figure out where i'm not (on).
I prep when i hand piece- i draw my 1/4" lines on my pieces- it only takes a few minutes- it makes all the difference and it speeds up my sewing time- i can put together a block in at least 1/3 to 1/2 times faster- including the line drawing time when i do the prep- and the blocks are precise.