So OB told me the wrong blood type

Today the OB told me I’m a AB- and need an RH shot with the blood sugar blood draw at 28 weeks.... I was like wait I’m an O+??? So I called my mom and she’s like it’s impossible for me to be AB or even a negative. There are no negatives in my family, both sides. My parents are A+ and O+ so how the fuck did they get AB??? Not to mention there’s not a single negative in either blood line.... idk what to do 🙃