Internet Speed

On the Xfinity app, it says my plan is for 600 mbps after the complimentary speed upgrades. When I go online to xfinity.com, it says that my speed is up to 150 mbps? When I test my speed, I am typically around 150-180 mbps. If I am supposed to be at 600 mbps why am I not even getting half of my speed? I understand that I am not going to be always getting the top speed, but I feel that it is an issue if I am not even getting half of it.