This can sometimes alleviate the problem (which is caused by some aspect of the way canvas is used to display the map, as I understand it): Make your page one square larger all around (two squares is even better). Give that margin to your map. Lets say you have a 20x20 map, make the page 24x24. Give your map 2 squares of margin on all sides. This can keep the map from "sticking" to the side. As a bonus you can use regular fog of war to mask those edges, and keep surprise tokens, reinforcements, invisible tokens and more out there.