I find the best way to cut is with a metal straight edge and a scoring knife made for acrylic or plastic.
Score the piece over and over again until it just snaps gently in your hands.
You can pick up a finishing knife or scraper at the plastic supply store with the scoring knife and Weldron. Sand paper works really well too.

If you can't find any of these tools close to you, there is a plastic supply near by to my house I would be happy to go buy the supplies and mail them to you.

I've done multiple DIY fabrication project recently and it is alot of fun and easy with the right tools!