It it is entire seams or if it makes the blocks fit wonky I'd do over. Even though I'm an open presser in this sort of thing I just do a new seam and fold over.
But like Maviskw says, if the fabrics are fitting together and well woven and not fraying I wouldn't worry my head too much about it -- for an 8th. Anything less than that and yeah, I get worried.
I'm not very impressed with the workmanship of one of my current projects. I have a sewing superstition about doing all of a project on one machine and had to switch machines. The transition as I was getting used to the different machine shows on the backside but nothing I think that will really impact the finished project.
Are you using a tight stitch? That also makes a difference. I use a smallish stitch and sometimes that can cause more problems than I solve if I try to take it out. Plus I have vision issues so whenever possible I just cut a new piece and go on.