Cutting out panels
I am trying to cut panels out of polyester for an umbrella canopy, but am having trouble getting a straight, non ragged edge. They measure ~ 11"(base) x28"(high). I layed the material on the floor and taped it down, with just enough tension to keep it flat; Then I put my cardboard template on top and traced around it. After removing the tape, I cut the triangles out, only to find that the edges are not straight, but ragged and irregular. Would someone be so kind as to tell me how I can do this and get straight edged perfect triangles?