Measure all of your blocks, are they all the same size?
If not, you can resew a seam here and there to fix them, or you can square them all up to the same size before sewing them together.
I prefer to square up/fixing the blocks rather than trying to square them up after they are being sewn together into bigger blocks or strips. If you wait til this point, you can end up losing part of the design element, points, etc...