I think there's false positives all the time with these tests, @redheadbride15 is more of an expert in this area but I've read a ton about false positives.
It depends on exactly what type of test you had. If you had the serum screening test (which is what most women under 35 are offered) then there is a very high false positive rate. Look at your test results carefully - they'll probably say something like 1:100, which would mean there is a 1 in 100 risk of having a child with Down syndrome. If the normal risk is 1:500 for your age then that's considered an "elevated risk" even though the actual risk is still pretty small. Your doctor's office should help explain exactly what the results mean. They may also offer a more accurate follow-up test like a cell-free DNA test or an amniocentesis.
Me: 40 DH: 43 Married 5/30/15 TTC #1 June 2015 BFP #1 9/28/15, EDD 6/10/16. DS born 5/23/16! TTC #2 May 2017 BFP #2 m/c 11/18/17 5w5d BFP #3 12/17/17 EDD 8/25/18. It's a boy!
Re: Higher risk..
Married 5/30/15
TTC #1 June 2015
BFP #1 9/28/15, EDD 6/10/16. DS born 5/23/16!
TTC #2 May 2017
BFP #2 m/c 11/18/17 5w5d
BFP #3 12/17/17 EDD 8/25/18. It's a boy!