How do I go about asking my OBGYN for another growth scan?

At 30 weeks my little one was measuring in the 13th percentile. She scheduled another scan for 34 weeks.

- I have had issues with my placenta before, subchronic hematoma.

- My baby also has cysts, incidental findings.

So, I am worried there is an underlying reason as to why she isn’t growing well. I have a 32 week appt, and would love to schedule a scan for then as well to just get rechecked. A month seems too far out. How would I go about asking? or Am I just overreacting?