A dental issue, please help

About two weeks ago I went to my dentist to get a dental flipper. She had her assistant did the impression for me and then send it to the lab. When I got my flipper, it was very lose and the assistant put some adhesive on it to tighten it. It was not good. So I went back again to adjust it today. The assistant put more adhesive on and made the tooth shortened. I I think it looks worse now. Can I ask the dentist to redo one for me without  any charge?  How should I talk to the dentist about this?Thanks for all your advice!