It's a tricky one. Given your age I'd say just go for the NT & see what the result is. Then again it is only a screening test so it's not like it gives you a result, just a risk. I had a similar experience to you but opted for an amnio. I think if I was pregnant again I'd ask if I could just skip the NT & go to the amnio, but I am almost 10 years older than you so my risk is going to be high regardless.

Don't think of it as a false positive cos there's no such thing. It only gives you a risk factor therefore you were not given a false result.