Use a Blind Hem Foot for the topstitching. All you have to do is move your needle position over to the place where you like your topstitching to end up and sew ( I just move mine over one needle position). It is a lot easier than using the edge of your foot. It's a much easier way to keep your topstitching straight. The bar in the middle of the hem foot will fit nicely in the seam (if you are topstitching near the seam). It's also nice to use for edge topstitching. All you have to do with that is use the bar next to the edge of the garment.