Dr. said i have small tear in placenta at 8 weeks pregnant. should i be concerned?

No: I am assuming you are referring to a detachment of the placenta from it site of implantation that results in a 'subchorionic' bleed or hematoma (blood clot). There is a small risk of miscarriage depending on the size of the bleed/detachment. However, in most cases the bleeding goes away on it's own and most women go on to have a normal pregnancy and healthy baby.