well since you already had the 3, i wouldnt personally worry. i assume you got the first to determine fetus size which is important in regards to those blood tests being accurate. but technically, that scan, and your other 2, werent necessary. if you were concerned about ultrasounds in general, those are the ones you should have skipped. as for the anatomy, that is really the only important scan. if there were any issues visible on the scan, your doctor would be better prepared at birth to have any necessary medical equipment or specialists on hand.
pretty much everyone gets the scans. there shouldnt be a worry for having one or 2 scans. the main worry would be for someone owning a machine, scanning weekly. even that is controversial as far as what, if any, harm would result. tihngs are often not detected until the anatomy scan. heart issues especially would rather be detected before birth, rather than wait until your baby who appears fine at birth, starts to have issues. the delay could have consequences.
dont worry about the scan, when you see your baby on the screen appearing healthy, you will feel reassured they are healthy, and that will take a weight off your shoulders, rather than the unknown. good luck