Extra anatomy scan?

I've had my last proper scan at 20 weeks. Since then I've had plenty of ultrasounds but they were 2 minutes long at best.

The baby measured a bit ahead at that 20w scan and now he is a bit behind according to the 2 minute scans. I wonder if that's accurate. I've been sick quite a bit since the 20 weeks scan, and I would like to see how baby is doing.

Has anyone done an extra anatomy scan privately? I am in my third trimester.

Are there any risks related to this? I think there shouldn't be but still want some reassurance.