I always thought that I was sewing a true 1/4 in seam until I made a project where it HAD to be an truely exact scant 1/4 inch seam. My 1/4 inch was off just a tiny bit. Luckily I corrected it before I had a nightmare project. I use a 1/4 inch foot buy it wasn't exact, I have to move my needle position a little bit. Ckcowl has good advice. Work on it until you master the seam allowance. You will save yourself a lot of headaches later on. On the simpler patterns it is easier to fudge a little to make it work. But as you make more difficult patterns it becomes more an more important.