If you ever need to cut plexi instead of glass to show off your original art here are some helpful tips. You can get a cutter from your local hardware store in the same aisle as the plexi. I purchase the thinnest plexi. Then I remove the plastic covering on one side. Then I use a ruler and permanent marker to mark my guidelines. Remember you'll want to cut the plexi slightly smaller then your marks so it will fit in the frame. Then I put a piece of foamboard or cardboard under the plexi. The side that you removed the protective cover should be faced up. Then with the ruler as a guide, press down firmly on the ruler, then start to score. I score it 12 times. Then I flip it remove the cover and score the back 3x. Then carefully pull the opposite sides of the plexi together. It should easily snap!
To remove any marks from the permanent marker just use a little paint thinner to remove.