Mirrored Acrylic cutting Problem

Hello Guys,

I am new here and a Problem with my 50W CNC Laser Machine from Chine. Aftet Cut, i get not perfectly corners. I upload an example here .

I use RDworks with the settings for tickness 2 mm Acrylic Mirrored ;

Speed 13
Power %65

I did not change the settings from this Machine. May be i must change somethnig . I hope someone can help me. Thanks .