When I wanted seams to match up I put one pin horizontally in the seam allowance and flip it open and check my alignment, then I tend to put 3-5 pins close to each other in that spot. I then sew a block or two, stop with my needle down and check the first block, sew another, check again..... that way if i do not like how one looks I only have to rip out a block or two instead of the whole row. I am a newbie so I tend to do a lot of checking as I go, love/hate that seam ripper LOL