Myriad prequel

Hi so sorry if the question seems foolish but bc I am 36 I took the myriad prequel test my dr messaged me that the Down syndrome screening came back negative and if I wanted to know the gender . I am happy but I also thought they that test tested for trisomy 18 & trisomy 13 am I wrong ? Wouldn’t she have said if something was wrong thank you for your help. Has anyone else done this test as well ? Please please any advice would be helpful