Welcome to HCM.
You have certainly done a dumb thing. Let alone Marijuana, smoking
anything in pregnancy
is harmful for the baby. You are more concerned about it being detected in the blood than the health of your baby. It will not stay in the blood for 10 weeks, but that should not encourage you to go at it again. You should be more concerned about its ill effects on your child in the womb. Say good bye to Marijuana for ever.
Wish you a very healthy baby.