do you have anything on the back of your ruler so it doesn't slip? Sand paper dots, or there are other things sold in the quilting sections for that. Then put your fingers on the ruler by where you are cutting and "crab" walk your fingers up the ruler as you cut. Cut only up to about even with your fingers and then walk them up higher and continue cutting, and do it again if necessary. usually you only have to "walk" once or twice.