These scans might be inaccurate sometimes so try not to stress yourself out mummy! Sending over positive vibes... But if you want peace of mind why not do the amniocentesis like your doctor suggested? May I know why you're not keen? My baby didn't have the same issue but was very small overall (below 5th centile), was born only 2kg but is now thriving and amazing.
Go for another detailed scan. Dr Ananda from Camden medical is an expert for infant anomalies. He charged me around $600 in 2016 for my detailed scan at 22 weeks.