It looks like you are over cutting the facets. You should get a good beginners book like “Facet Cutters Handbook” by Edward J. Soukup. From the info you’ve given it’s not clear if it’s you or your machine.
A beginner’s book is a good idea, but I strongly disagree with the suggestion of Soukup. It’s way out of date and describes procedures that most faceters abandoned years ago. Much better is Tom Herbst’s “Amateur Gemstone Faceting, Volume 1”. I also recommend volume two for more advanced topics.