marginal placenta !!!??

So I'm 19 weeks pregnant and I got told today that the umbilical cord is on the side of the placenta instead of the middle and I'm freaking out. My doctor wasn't in and it was my monthly check up so they had another doc explain it and she hardly said anything. I'm just stressing because this is my first baby and I don't want anything bad to happen. Did anyone else have this problem????? How rare is it ??? Will my baby be ok???? Pls help