GCT testing

Patient: Hello I am 41 yrs old and 28 weeks pregnant.i have taken an 1 hour GCT test and failed.Now i have to take a 3 hour GCT test in four days,well my nurse told me to eat a regulary meal also eat a candybar around 4:00 everyday for three days until my testing but fast after twelve am the morning before testing.How do i prepare for this test.