I took a class with Carol Doak and she taught us to do few (3 or 4) basing stiches over the critical, need to match areas. Then you can sneak a peak and adjust if needed. On a large block like you are doing, do not break the thread between each basting area but just skip forward to the next critical spot. When you are happy with the basting adjust to normal stitch and stich over the basting stitches which you will just leave in.