U.K. Scans

So just got my first appointment. I will be 13 weeks 4 days on scan. Managed to be brought forward to 12 weeks 6 days. They were not happy but I want the double test for Down syndrome risk which means scan needs to be completed before 13 weeks 6 days. If my dates are slightly further on I won't get this test. Just means I need to see consultant after scan on a different day which doesn't really matter. Just helpful for first time mums to know this if they want the test done that your scans are not too late