Your seams are likely a little too wide. That makes your blocks short for the length of the sashing strips. I would measure your blocks and adjust the cut-length of the sashing strips to match the unfinished length of the blocks.

Actually, if you have already sewed the sashing strips to the squares, all you have to do is remove one seam (say, on the left side of each square) and re-sew to make the sashing length match the blocks. I would re-sew first and make sure everything is accurate before trimming the extra sashing from the seam.

I am assuming that you have assembled the quilt in rows, with the blocks in one row and the sashing strips in a separate row.

Hope this is clearer than mud!

I just looked at my machine to see about changing where my needle is and the only way I can do it is if I do a different stitch entirely.

There should be a stitch width setting that allows to do a narrower or wider zig zag. If you change that when your machine is set to a straight stitch, it should move your needle one way or the other.

If you can't or don't want to move your needle position, you can use a stack of post it notes as a guide for the correct seam allowance.

The other option is to move your fabric. Instead of using the edge of the foot as your seam guide, perhaps mark a line inside the edge of your foot to use.

What I do is cut moleskin strips (moleskin is in the foot care area of pharmacies), which have an adhesive backing, to the bed of the machine and butt my seams up against it.

Welcome to the board from Southern California!!!
Looks like your're getting lots of great help already!!
Looking forward to your posting the quilt when you have it together! It's going to be beautiful!

My machine is a Brother LS 2125i. I'm looking at the manual online and not seeing a way to fine tune the needle. There is apparently an option to do different stitch lengths with the needle in the middle, or just one stitch length with the needle to the left. Now the lines on the needle plate, are they based on the needle being in the center position or left position?

ETA-Looks like it's based on the center position. Not that they are labeled with numbers or anything!

Sounds like you have a machine with set length and width for each stitch. At some point you will want to graduate up to a machine that has variable stitch length and variable stitch width, plus independently adjustable needle positions.

In terms of working on the quilt you have posted, now is not the time to be changing your needle position and seam width. Until you finish this quilt, I would keep everything as you have been doing it. Just adjust the sashing strip lengths (shorten them to match your blocks) and you are good to go.

More than likely it is based on the center position. I would take some sample squares and stitch 1/4 inch seams and measure to see what it is compared to what it should be. For example 3 pieces that are 2" in width. Stitch together and see if it measures 5" I always do this with my students when I teach beginning quilting, before we even stitch their first blocks.

I agree.

I think this might be the case as well. Do you measure each block as you go? This can also help with matching up those sashing cornerstones. If your blocks are of unequal dimensions this will make matching up the sashing to them near impossible. With blocks a tad to big you can sometimes ease them to fit your sashing but if the blocks are too small you can maybe stretch them by blocking another 1/8" or so. anything much more then that can cause problems for you.