That is so easy to do...I took take photos and take a last look before making the sandwich. Just this weekend I was guilty of switch two blocks ...when I worked on quilt the placement of the colors were so important to me..then I must have flip blocks as sew top seams instead of bottom seams...thus making the block in wring place. Luckily the were outside blocks so easy fix.
Glad you also found you problem
Judy in Phx, AZ