Sandra-P - the worst I've done is to look at it and realize it's wrong, rip out and sew correctly, only to realize I was looking at it wrong to start with and it was Ok - so it has to be ripped out and put back the way it was to start with.
Those are the times I decide my brain needs a rest and it's time to move away from the sewing machine (and anything sharp too).
I've to the part of assembling the blocks, and after that is the fun part of getting the arranged correctly.