Evaluation of ssd_512_mobilenet_1.0_coco on COCO validation data set

I am trying to evaluate the “ssd_512_mobilenet_1.0_coco” on COCO validation data set. In the model zoo of gluon cv they mentioned the AP as 21.7/39.2/21.3. But I am not getting this, I am getting only 2.2.
Please share the inference script for all the 5000 validation images of COCO 2017 dataset.