Glucose test first trimester

I'm over weight so my docto put in to have a glucose test during the first trimester. She didn't tell me to fast she actually said just eat like normal. When I got to the lab the tech told me I'll fail because I ate cereal for breaat fast and probably have to come back for the 3 hour test. Ugh Anyone else have to have a glucose test in the first trimester? Did u fast?