Notable calcification of placenta 24 weeks 4 days

A little back story on this issue. Baby has been measuring small about a week behind considering my last menstrual cycle due date(january 13th) all along. At my 20 week scan they noticed she was in the 6th percentile with a due date going off my last menstrual cycle. My very first ultrasound (not with my regular doctor but done around 9 weeks) my due date was a week after (january 19th) going by my cycle. So taking that into consideration at the 20 appointment my doctor said lets change it and it put her in the 33rd percentile which is great! Now 4 weeks later I had another scan just to make sure shes growing on that curve. She is now in the 18th percentile and they also noticed I have a marginal cord insertion to the placenta. What should be 3 cm from the edge is only 1 cm from the edge on top of having noticable calcification of the placenta. So dropping more makes me nervous especially 33rd to the 18th. I'm just curious if any one else has had calcification this early on and if it was an issue. Shes scheduled me for another scan in 4 weeks but if course I'm freaking out because I know how important a healthy placenta is. She said you dont usually see calcification this early on so I'm super nervous considering all the other factors. Also I dont smoke nor have I this entire pregnancy which is typically the cause for early calcification. Any input?