This is my first pregnancy. Today I was supposed to go to my ultrasound they were scanning for Down syndrome ( I'm 12 weeks ) since I missed that, earlierst I could book was next week and by then ill be 13 weeks? Should I still be getting the translucency scan?? Or what should I be asking for ?

Your doctor should be ordering what tests you get, So you need to discuss this with him
But one week should not make that large of difference, even conception dates and due dates are estimates and can be off a week in dating