Depending upon the canvas dimension, make 9 or more sections with washi tape. So, when you start working on a section, the tape will act as a guideline to cut the plastic from only that section without exposing the rest of the location. Here's a variety of four-star and 5-star https://best-diamond-painting-sto84937.wikiworldstock.com/628359/new_step_by_step_map_for_online_store_diamond_painting