Down Syndrome Test

I just received a call from doctors office informing me that my DS test came back positive with a 1:184 result. They said this was not a definite yes or no just a screening. I am 24 the number seems to be off to me like they messed up my information somehow. I go in tomorrow for my 20wk/anatomy scan and they will discussing everything more with me then. Anyone deal with this? And does the numbers seem right? I don't know a lot about this.