Don't cross the border. Are you laying out your rows with a double pointed checkering tool. There is a file you can use to sharpen your points and work in border areas, after you lay out our rows. You can also use that file to ease up to your border, so you don't cross it. While I am not an expert at this, and haven't done it in a while, I use to start with a shallow border then go back over it later. Usually when you go back over it, and make it deeper and wider, it helps remove slight over runs, providing they aren't too bad.