I was wondering if the baby keep measuring four weeks off, would the doctor induce my labor or its nothing serious just yet ?

Depends: If the baby is, indeed, not growing inside the womb (iugr: intrauterine growth restriction); then, generally speaking, delivery is considered. However, this diagnosis (iugr) can be a tricky one to make and really needs a solid foundation (e.g. History, physical exam, work-up/ultrasounds, etc..). You need to have a thorough discussion with your ob/gyn.