Reassurance needed

Im worrying a lot. I found out i was pregnant later on than most - took a test at what would've been 11 weeks, got a quick scan at the health clinic 2 weeks later where they told me I was measuring at 13 weeks (doesnt even look like a baby to me). I didnt know how far along id be and it was scary to be told I was that far without symptoms. I havent had any official appointments with the maternity hospital. Finally managed to get a phonecall where they went through the questionnaire part and im to expect a phone call later in the week to book in the blood tests etc. On this call the lady was saying im too far along and missed my first scans and they'll try to rush me on the system to get the second but i may have been too late for the screening tests for Downs Syndrome etc. Im about to enter my 15th week and im just scared ive already (unknowingly) started off badly. Realistically I should be a low risk case but im just worried everything is going to go wrong and not being able to get the tests is a massive concern. Can anyone explain the difference between the various NHS scans and appointments. Would an anomaly scan pick up health concerns etc? This is my first pregnancy and I feel overwhelmed already.