Place a cutting mat, which you can buy in the scrapbook section of a craft store, on the table.
Place the top of the vinyl board on the cutting mat. You want the entire edge of the board to lie across the mat so that you can trim it evenly.
Place a yardstick or ruler across the vinyl board, ensuring that the yardstick or ruler is straight.
Roll the rotary cutter across the length of the vinyl board. When you get to the end, pick up the cutter and place it on the beginning of the vinyl board. Roll across a second time. The vinyl trim should come free from the board. If it does not, cut across the indentation of the line you have made previously with the rotary cutter.