Isn't it always the way, the seams you need to un-do are the ones you used tighter stitches or back stitched at the beginning and the end?
Someone here said not to be cheap with seam rippers - buy good sharp rippers and keep one by each machine you use, one with your sewing basket and still one more in the supplies for when you misplace one. (Yes, I have 5 different seam rippers because I have also grabbed the closest sharp item and lived to regret it.)