Blood test gender ?

How many times have they been wrong ? I’m not pregnant or anything but I was curious because my second baby I would like to have this done an I’m very weird an think about things way to early like this for example lol how many weeks were you when you got it done ? So I have a baby girl and when I’m ready I would love to try for a boy an maybe do things different than I did with my daughter. Everything was kinda last minute with her an I don’t want that again.