I'm Four Months Pregnant I Just Had My First Doctors

I'm four months pregnant I just had my first doctors appointment last tuesday I told them that I smoked weed and that when I did I didn't know I was pregnant but now I go in four weeks to my next doctors appointment and I will have a drug screen and I smoked on this past sat the end of Sept. And I'm scared that it will be in my system and they will call cys on me and my baby isn't even here I had some stress before finding out and day into finding out and don't want this stress of loading him or her do to my mistake