Best investment for my sewing room was a battery operated seam ripper. I learned about it on this board some years ago. It has saved me hours of time, and it never yet has damaged fabric. You have to start the first several stitches with a regular seam ripper, and then this little gadget breezes right through once you get the technique, which isn't hard. You hold your seam open firmly and cut toward the thread between the two layers of fabric. You can clamp far end of the fabric down if you have a long seam. Since I got that I have been much more willing to tackle fixing my mistakes. Needless to say, it gets a lot of use. Don't quote me, but I suspect that any mustache trimmer would also work, including the ones for dog muzzles, so you may already have one around the house. Test it on some scraps, though, especially if it's not sold for this purpose. All clipper blades have to be oiled regularly, so be careful not to get oil on your project.