How accurate is the blood test for gender?

Found out we are having a little boy 😍😍😁😁😁 we are over the moon, this is what we wanted...we have a daughter already! Lately I've been hearing things that the blood test isn't 100% ?! I go for my anatomy next week  and I'm worried baby boy Moore will actually be baby girl Moore.......Obviously we will be happy either way but I am just curious what's been everyone's experience ? I had my blood drawn at 13 weeks  idk of that matters or not.....thanks for the input! I appreciate it 😊