The more experienced one is with a sewing machine, the more accepting one is of the need to sometimes unpick and re-do. Practise making perfect (and it's not because we practise for the fun of it!)... experienced sewers are FASTER at unpicking.
Here is one trick I've discovered that a lot of people DON'T know....
1. Get a good seam ripper - fine-point and super-sharp. I think I may have mentioned that I'm in love with my Clover Seam Rippers...
2. Unpick any backtacking/backstitching or multiple rows of stitching with care - don't rip through them as shown below. Cut through a few of the individual stitches and pull the threads out.
3. On a straight seam - ONLY IF YOU HAVE A GOOD SEAM RIPPER - you can gently slice through the stitches as shown below. The longer spike on the seam ripper goes to the top and the little ball on the underside. You shouldn't need to use any force to cut the stitches.
So.... what do you do with all the little bits of thread left in the fabric? Pick them out with your fingers...?
Roll it on the right side of fabric...
I get excited about things like that.