Anomaly scan at 23 weeks?

My baby is due September 17th and I originally had a scan booked for the anomaly ultrasound which I had to reschedule due to university commitments. Now I've been told the scan won't be until May 17th, isn't this a bit too late for this type of scan? I asked the receptionist but she was rude and unhelpful. I could really do with some advice, this is my first pregnancy and I feel totally ignored :(