I was looking recently at a professional's quilt which has won prizes. My eyes after scanning the whole quilt zoomed into a section where her sashing stripes did not line up. Only about 1/2" off but even non perfectionist me would have had to alter. Some not lining up I can live with I was amazed this caused me so much of a problem.

I would follow all the above suggestions and make it right. An extra wide outer border which you could trim down to a size you want may be helpful, although it is the inner runs I find cause most problem. Another solution is to offset deliberately each row by 1/2 block size with a plain block.

Recently a a teacher told us in a class that put corner squares along your sashing even if it was the same fabric as the sash and your smashing would always match.