Can the plastic tray be sanded down in way it is not sticking out? It's cutting like a knife. Under my tongue is hurting bad.

I had my first tray put in yesterday, went back today cuz one attachment came off and to sand down edges as it is cutting up my mouth in diff. Places. It was somewhat fixed but. But other parts still cutting and it stings and hurts and I am diabetic, I cannot be getting cuts like this in my mouth. I am very frustrated and discouraged as well as worried. How can tgis be fixed, how much more needs to be sanded down or is there a way to sand it where plastic is. Nott sticking up, cutting my tongue. It hurts!