I've been taking a centrum everyday for the past few months, i found out that i am pregnant 8 weeks can this have harmed my baby since it has vitamin a?

NO CHANCE: Congratulations! Vitamins A is an essential nutrient important for having a healthy baby. Excessive doses (more than 10,000 iu/day) are associated with increased risk of birth defects. Centrum has about 2500 iu of Vit A, well within the safe range. See http://bit.ly/1khXuAE for details. The good news is the Folic Acid in Centrum has significantly reduced risk of neural tube defects.