Smoking while pregnant

I am 4 1/2 weeks and have put down the cigarettes today. I told myself no more smoking because I don't want to harm my baby or have a risk of miscarriage because I would blame myself forever. But this is so hard, I've been a pack a day smoker since I was 15. My brain is trying to talk me into lighting one up. My addiction keeps telling me "you're only 4 weeks, it's just a ball of cells, you won't do any harm" and also "most women wouldn't have even found out they were pregnant this early, you'll be fine." I want a healthy baby, but quitting smoking is so hard!! God give me the strength to do this!!