I'm a single dad, my daughter is 18 but she acts a little contemptuous and just?

First of all teenagers are one thing, but she is an adult now, and you can't do anything to change the past. The best you can do is to sit her down explain what could happen and hope you set a good enough example that she will make the right choices. As hard as it may be to admit this your baby is not a baby any more. She needs to experience her life, and make her mistakes along the road....always be her daddy and be there to pick up her fall :)