This happened to me in the beginning when I made spice labels for the first time. Sometimes cleaning off your blade or changing the pressure will fix it. If you don't want to abandon the cut you've already made you can use a second weeding tool to hold the letter down while you use your other weeding tool to lift up the extra vinyl. It could also happen becasue your vinyl letters aren't sticking to the backing well which can happen so holding it down with the second tool can help.